Heimerdinger is a much more complicated character to play than a lot of people who dont play him think, and a lot of his play is down to personal preference and intuition. Ill give you some tips however.
Start turrets, then grenades, then missiles, then another point in turrets, then max missiles. The second point in turrets doubles their cannon damage to make it easier to CS and give an early zoning advantage, but leveling them first will get you killed except in rare situations, such as if youre laning against a tank or Jax and the enemy jungler is an Udyr or something similar. After that, youll either level turrets or grenade depending on your playstyle (see my items advice to follow)
When placing turrets most inexperienced players will tell you to put them in the triangle of power, and it is a good way to place them in most situations. Put 3 turrets so they all cover each other but theyre too far away to be aoed down at once. This does a few things, it prevents them from being aoed and it also gives you a large radius where your speed is increased for kiting. However its also the easiest formation to play around: picking off one at a time with poke is very easy, and leaving the radius leaves you completely defenseless.
Depending on the situation, there are a few other ways you can place turrets to optimize their effectiveness. If youre expecting to be ganked a lot or are facing an opponent whose gap closing consists of running at you, you can place your turrets in a line going back to your tower. This allows you to use your turrets as a jetstream to run to safety whenever necessary, but leaves you more vulnerable to all ins because your turrets wont all be able to shoot the same target.
You can also place them in a straigh line across lane, which prevents them being poked down by line skillshots, but youre committing to fighting in that case as you have no speed boost to run away.
In very rare situations, typically against Jax, Irelia, and certain other opponents, you can stack all 3 of your turrets in one place. This leaves them extremely vulnerable to being destroyed by any multi target spell, but punishes any opponent who has to get near them to destroy them. Irelia in particular will stay in the same place when destroying them instead of dashing all over the place, making her much easier to land a grenade on. This formation will leave you almost no room for kiting, so when utilizing it you either want to defend your turrets from a distance and be prepared to fall back, or be confident in your ability to burst your opponent down before you die.
For runes, there are 3 keystones which are most valuable: Electrocute, Comet, and Dark Harvest.
You use electrocute in any situation where a large number of your opponents are going to be all in type characters, such as Yi or Irelia. Turret shots count as triggers for it, but each turret can only give one stack so an auto+2 turrets can trigger it in laning, though most commonly youll trigger it with a grenade and 2 turrets or a grenade a turret and an auto.
Comet is used in any situation where your opponent is hard to move in lane or most of your opponents are hard to kill with burst, such as a tanky comp. Turret shots can both proc comet and can recharge it, meaning an opponent moving through your turrets during teamfights will recharge it insanely fast. When using comet you should be looking to force opponents out of lane and doing a supporting DPS role in teamfights, not going for flashy 1v1s, as your burst damage will suffer compared to electrocute or DH. In comparison to aery, its damage is higher thanks to turrets recharging it and it being AOE, so aery is almost never an option.
Dark Harvest is only for people who feel confident with Heimer and have a lane where they can either win early fights without electrocutes damage, or want to just focus on farming minions and farming souls off the opponent. Remember that a 15 CS lead or 2 tower plates is roughly equal to a kill, so you dont need to be dominating your opponents KDA to be winning lane. In comparison to electrocute, DH has the potential to allow more multikills in teamfights to allow you to carry better, but relies on you to be good enough to charge it up or its worthless. Since turrets can proc it, it can catch opponents off guard who think they know your turrets damage and when its safe to walk past them only to be executed by DH.
For other runes, Mana Band is almost mandatory, and many people swear by increasing your CDR as much as possible with runes as well. Ravenous Hunter allows you to siege more efficiently and solo the baron as early as level 13. If youre going a first buy Zhonyas, commencing stopwatch is of course very good. Taste of blood goes a long way to making you immovable in lane without jungle ganks, and scorch likewise helps move opponents out of lane.
For items, your starting items can be similar to anyone else, but I personally prefer a dorans and a control ward. Heimer can usually control his lane opponents very easily, so his biggest threat is ganks he didnt see coming. Since you can keep your opponent shoved easily, keeping the control ward alive should be very easy, and will give you time to make a plan to deal with any incoming gank, whether it be running to safety or getting an easy double kill.
For first buy, depending on your playstyle and opponent it can be Ludens, Morellos, Liandrys, Zhonyas, or RoA.
Ludens is bought if youre in a lane where poking your opponent out of lane is the best way to stop them from scaling, as its mana will keep you in lane and its extra damage will force tanks and the like to recall much earlier than they would like to, and help gib all in assassins. Its a good safe buy for any situation.
Morellos is of course bought if your opponent has a lot of healing on their team. Its not as strong of a choice as other first items so make sure if you buy it youll get a lot out of it, meaning more than one significant healing source on the enemy team. Dont be fooled into buying it first item when laning against a Vlad, as the reduction in damage will not be made up for when he all ins you and in poke wars he can wait for grievous to wear off before healing.
Liandrys is for going the carry Heimer route, as it allows you to leave your turrets at 2 and max grenades second for maximum damage while your turrets remain competetive by proccing Liandrys constantly. Youll do by far the most overall damage with this build and be able to burst effectively, as well as being effective at fighting even with 1 or even 0 turrets in some situations. However positioning is very important with a Liandrys first build, as after your initial burst youre very vulnerable to death because your damage is extremely over time. Make sure you know where you stand in teamfights and you will carry them.
Zhonyas is the classic first item and for good reason. It plays into heimers fantasy of maxing turrets first and gets rid of his weakness of needing to stay in a specific area by letting you stay in that area while punishing enemies who are there. However, remember that by using this build you are trading reliable burst for survivability: you actually have much more burst than the max missiles and grenades first build but ONLY when your turrets are up, so if your opponent can poke them down before engaging you or is strong and smart enough to destroy all 3 while youre Zhonyad, youre utterly helpless and have only delayed your death a few seconds. When going Zhonyas first you will be 1v1ing only the dumbest opponents and mostly be focused on teamfights, and will likely be dedicating the rest of your build to CDR to make sure you always have turrets available and rockets to fire from safety. However, it is a tried and true build, so dont be afraid to use it, and definitely get an early Zhonyas if facing certain opponents like Zed regardless of other items.
Rod of Ages was recently buffed by having its combine cost reduced, and was already one of the most efficient items in the game. It caters to no specific playstyle, and has a lot of downsides to the more specific ones, but will give you a mid game power advantage. Its mostly good for if youre planning on split pushing, as the overall stats will allow you to 1v1 efficiently with any opponent.
After your first item and boots you will either rush banshees or zhonyas if the enemy team warrants it, or a good thing to do is to build Magpen. You can build just the oblivion orb from morellos and then go void staff, which will give you a lot of damage especially if your first item was Ludens or Liandrys. In certain situations a Rylais can also be very powerful.
For your Ult: ult turret is for opponents who will be crippled by the slow, when youre caught in teamfights with mostly tanky opponents who wont destroy it quickly, when denying an area, or for soloing baron. Ult rockets are for killing a squishy opponent who jumps on you. Ult grenade is your most commonly used ult, used to finish off fleeing opponents, trick engage opponents who are cocky, thrown after your opponents engage to cut off part of the enemy team from the fight while your team kills the engagers, or to stun an entire enemy team for quick cleanup in the right situations.
Never waste your grenade, always throw it carefully and land it. A missed grenade is a dead Heimer.
Never throw your missiles and grenade at the same time except in the direst situations or when the kill is already secured. The trick is to throw the grenade, wait half a second for your turrets to fire their lasers, and then fire missiles to charge a second set of lasers. If your missiles impact before the turrets have fired their lasers youre wasting a huge amount of damage even if not maxing turrets first because they will not remember the charge.
And lastly, for a cheeky move you can very easily steal the enemies topside buff by placing 3 turrets and tanking 2 hits for them, then retreating behind the turrets. Replace a turret after the first one dies and auto on cooldown, but do not replace any more except in emergencies. You may need to kite the last hits.
If you have any specific questions ill try to answer them
