CS above all else. Learn to get maximum last hits before you try to start trading, but as far as trading is concerned a quick tip is to abuse a level advantage the moment you get it, quickly level a skill and start a fight, you have higher stats during that time so unless its a particularly bad matchup you should win the trade and set them back. The most powerful level advantages occur at 2/3/6.
Its not your job to roam, its your job to farm so you can frontline for your team, dont feel obliged to teleport botlane unless you see a prime opportunity to get your team kills, otherwise as you said you will return toplane to find your opponent 30 CS ahead of you and you have nothing to show for it.
Unless you're playing someone like Riven or Darius you shouldn't be concerning yourself with kill pressure, for toplaners ignite is never worth the slot unless you know you need GW for that game. If you stumble upon a kill early on then that's nice but you shouldn't be missing cs or overextending in an effort to get one.
That being said, should you happen to get a big kill lead you should actually NOT try to take the tower early. Just recall and buy a damage item each time you kill them in lane, in low elo many players believe that their turret gives them protection against a 5/0 opponent, so they will keep coming back to lane and you can get more and more fed, ironically you want their turret standing for as long as possible if they are losing hard (mind games play a huge part in league). If you were to take the turret ASAP then they would either go mid and grab assists, or sit under their inner turret and make it much harder for you to farm kills without getting ganked. I kid you not, many games I have gone 10+/0 with pre-rework Darius before the first tower fell simply because I never attacked it, and my opponent would keep coming back to me and get 100-0'd the moment they step out of tower range.
This strategy is used in the LCS too (called "Extending the Laning Phase"), because taking the tower too early allows a losing top to freeze the wave closer to their base where their teammates can come gank for them. You want to force a feeding opponent to come as far away from his base as possible for farm so that his midlaner/jungler can't bail him out so easily. I know it sounds completely counterintuitive to keep the enemy tower standing when you are winning hard but trust me on this. And before you say you want to start roaming early as possible, believe me when I say that you will be much more terrifying coming out of lane 9/0 than if you started roaming 3/0.
And ALWAYS ask your jungler before you consider starting a camp, and don't be surprised if he tells you not to. As a jungle main having one of the easy camps level up can completely screw my first clear depending on what champ i'm using. You seem to be a nice person but if you ever tell a jungler to "Fuck off idiot I'm doing it anyway" after he asks you not poach his camps (and yes, lately I have found quite a few toplaners/ADC's who act exactly like this) then don't be surprised if he intentionally avoids ganking you.