I have a few questions concerning top or mid laning. How often am i suppose to harass the enemy? If I am melee and the opponent is ranged, how can i not constantly get poked? When should I roam? Should I focus on farming or harassing my opponent more?
All the time. Or never. Depends on the laner in question. Akali mid for example has no way to follow up on harass pre 6, so she obviously shouldn't try to harass pre 6. Pantheon top on the other hand has almost no reason not to be chucking spears at people's faces, so if Pantheon is in a good position, it's almost always the time to harass the enemy.
Most melee champs have a form of hard engage, especially midlaners. For example, when Yasuo has his third Q charge, W, and E, he has a stupidly powerful engage tool where he dashes through minions to get on top of the enemy, using his Wind Wall to stop any projectile counterattacks, and using the knock up on his Q to kick off a powerful trade.
Okay that sounded really out of the blue, but think of it like this: EVERY action in lane is a trade. Every time the opponent uses a skillshot on you, you can retaliate by dodging it and then engaging on them. This is how really good melee midlaners, especially assassins, can win lane even against a ranged matchup. If you can negate even part of an opponent's damage through dodging, abilities, sustain or shields, etc, this opens up opportunities for you to jump back on the opponent and trade whatever they threw at you back at them. A good example is Katarina vs Ahri. If Ahri uses her Charm and Kat can react fast enough, Katarina can Shunpo behind Ahri and use her spell rotation. Ahri can't retaliate very well since she just blew her Charm, so even though Ahri is ranged in this matchup, it ends up creating an opening for Katarina.
Although you are going to have trouble in certain match ups (
vs 
), and certain champs' long range harass is just plain harder to deal with (For example Pantheon or Vayne top lane), but EVERY ranged champion has an opening of some kind. If you can capitalize on it, you win. (On the other hand, if you do absolutely nothing while the ranged champ harasses you, they win).
Depends. The super easy explanation is that CC heavy laners for example are perfect candidates for roaming, while damage based laners are more suited for just sitting in lane for extended amounts of time. The slightly longer explanation is, are you able to get anything out of a roam?
Your roam should both synergize well with others and have a purpose. For example, if I'm playing something like Malzahar, who's ultimate is absolutely devastating due to how long it can hold somebody down, I should be looking towards a lane with a large amount of DPS. Let's say my top lane is Maokai, and my bot lane is a Jinx and Lulu. Unless Maokai is very ahead of his laning opponent or for some odd reason is buying large amounts of AP, ganking top lane wouldn't be nearly as useful as it could be, as Maokai might not have the raw damage to crack through the enemy Top Laner's (usually) tanky shell, even with my help. On the other hand however, Jinx and Lulu's DPS is scary high even if they are only just even with the enemy laners. If I were to pin down the enemy ADC or support while Jinx and Lulu are ready to help, that's almost a guaranteed dead enemy.
Other variations of this exist. Most top laners run teleport and the auto attack based Top Laners are ridiculous at destroying towers. Let's say you're playing Tryndamere and that bot lane just had a big fight and everyone in bot lane just backed or died. If you think you can destroy the enemy tower before the enemy Jungler or the enemy bot laners can get to lane and stop you, this could be a really good opportunity to get your team a lead by knocking down the tower while nobody's there to stop you. Unless the enemy top laner can simultaneously destroy towers and out scale you (), this move, if done right, is almost always a guaranteed advantage for your team.
Focus on farming, with your mouse constantly hovering over the opponent. Farming is ultimately how you win games. It gets you gold which gets you items which makes you actually useful in the late game which always leads to good things, always aim to out farm the opponent in the long run (and I mean in the long run. Don't risk your neck to get just one more CS if it leads to you either dying or getting so injured that you have to back, as you waste a lot of time and thus farm getting back to lane). Ultimately however, harassing depends on the lane matchup as a whole. Pantheon should almost always be chucking Qs, many Assassins in mid lane need to learn how to take opportunities every time the opponent blows a cool down on a minion, everybody should take advantage of an enemy that overextends, etc.
How often am i suppose to harass the enemy?
Whenever it's possible for you to come away in a better position than your enemy.
If I am melee and the opponent is ranged, how can i not constantly get poked?
You really can't. If you want to farm, you're gonna need to engage with the ranged one and either kill him or make him fear you. Even going under turret won't really help. If neither of those are possible, ask for a lane swap or a bunch of ganks.
When should I roam?
EIther after you have both of your turrets down or when you see an opportunity to get free kills.
Should I focus on farming or harassing my opponent more?
Only focus on harass if it either stops them from getting gold entirely or gives you gold directly (as in, you're going in to kill them soon).
How often you harass is based largely on the champion you're playing as well as the positioning of your opponent. Unlike in the bottom lane where you can safely harass from behind your own minions, oftentimes a top champion has to be in your wave to harass you, or you have to be in theirs to harass them. At early levels, having an entire minion wave aggro onto you can deal much more damage than a champion can, so use that to your advantage. If it's a melee top laner, try and bait them into wasting skillshots on your minions, and when you can see that they're either low on mana or have just used up their abilities to farm go in, get a few hits, and then quickly back away so you don't have to walk back through a bunch of angry minions. Learn how to deal with champions who have serious early game advantages and lane bullies, because in cases like a Darius or a Renekton your best option is to play passively and wait for them to make a mistake.
If you're a melee and your opponent is ranged, there is no real way to avoid taking poke. They can stand behind their wave and hit you when you go to CS their front minions. As a result they farm safer and are more liable, like lane bully tops, to push the lane. This makes a favorable position for you because a ranged character will most likely have lower defenses and health, making them much more susceptible to ganks. Ranged top laners will usually have some form of CC, but no real escapes outside of Vayne or Teemo, and they won't have enough CC to run from both you and your jungler. Again, play passively, farm what you can, and take advantage of their mistakes. Consider building with a defensive focus, and taking a Doran's Shield, even if it isn't the best choice for your character, can mitigate the damage they're doing since most of it will be AA based.
Roam either when you've pushed your lane up to the enemy turret, or when you have completely taken it. Remember that if you free push to turret, you can pretty safely head to midlane for a quick gank in the time it will take them to push back to yours. Use that to your advantage to come in behind them and trap them between you and your oncoming wave. It's better if the jungler or the midlaner joins in when you head back to top lane.
The last one depends more on your champion. Someone like Darius or Wukong does a lot better harassing the opponent, and has ways to get CS while doing so (i.e. Darius' spin, Wukong's Nimbus Strike). If you're playing an aggressive champion, your best bet is to rush in, do some /quick/ damage, and then rush back. A good example would be Renekton, who's standard combo goes something like spin > AA > W > AA > Q > spin back. That's four hits, one of which is a brief stun that sets you up for the second AA, and then the Q heals you for a small amount just before you dash back, dealing damage the whole way. If you're playing a more passive top, you focus on farming. Passive top laners tend to have much stronger late games, like a Jax. Early on, Jax can have some difficulty, but once you build your first few items you hit a power spike and can then start going in much more reliably, and your skills have scaled up to the point where they're doing a good amount more damage.
The long and short of it is that the toplane is very much a tug of war. It's easy to get countered, easy to counter, and relies heavily on your own knowledge of positioning, of enemy champions, and map awareness. Your best bet isn't to learn any one way to handle top lane, but to learn how the champions you enjoy most handle the top lane in their own ways.
I'll give basic tips
How often am i suppose to harass the enemy?
Big question. Depends... Early game the minions have a big impact on trades. Clear a few more minions faster than your opponent and you should have windows where you have a level advantage. He should also have less minions for him on his side so if he steps out of place to maybe get farm (especially if you have a level advantage) punish him. I call this slow pushing. The slower you push the faster his creeps will die and draw him out to last hit, and the less he can turtle, but the less of an advantage you actually get in trades.
When your creep wave is bigger it'll push on it's own. You'd lose a lot of farm if you leave and they only last hit. Commit to pushing to their tower to reset the lane
If you push much faster than your opponent (maybe your champ has great area of effect damage) you are fast pushing. This is an okay way stalling the first few levels if you don't want to trade.
When pushing lane in many ways it makes it easier to handle your lane opponent, but it exposes you to the jungle ganks so use your wards!
Minions are less of a factor as the game progresses.
When you're playing Nasus you goal is to just farm stacks and build tanky. Your Teemo is a very annoying aggressive laner though.
If I am melee and the opponent is ranged, how can i not constantly get poked?
If your opponent knows what they're doing they can make your life hell if they slow push and punish you if you go for CS. Buy lots of potions, start flask probably and try to push harder. It really depends on your champ and theirs. Darius is really good at pushing creeps when against a ranged champ. With a flask he can stall a few levels and later after going back to heal and when he has his full combo he can lay down some punishment if Darius grabs them. Nasus on the other hand is about farming and enduring. He has little damage early so take teleport top lane to help sustain through... More sane option is to minimize your time in their range. When they auto attack you they should get minion aggro, minion damage can help you a little bit. Fun fact: auto attacking a champion will get you minion aggro, but abilities do not. I got to diamond without knowing this...
When should I roam?
Perhaps when your opponent is too scared to fight you in lane and is turtling at his tower, but you can't dive him, but it's too late in the game to bother to grinding out a cs advantage. When you push to their tower and are healthy you can probably do other stuff on the map.
