Hello, I'm Sayakus. I play as Heimerdinger quite some time and i think i can share some of my knowledge and experience.

I don't think that you will be some kind of immortal deadly Heimer by just following this guide.
Remember if you have bad movements, cant count to three and you are kills greedy as hell any guide will help you.

So let's get started shall we ?

btw

AP- Ability power
AD- Auto damage

Heimer is Heavy Pusher and AP disabler good for mid. But don't treat him as some kind of Veigar or Annie.
Long time passed since Heimer had more than two turrets so you should remember few things about turrets:

Turrets is your support not vice versa but don't treat them like creeps. Turrets grants Heimer early/mid game farming ability. They are great support in case you have to fall back so don't make some steady front line in front of you, look around sometimes is better to put them on back so you can fall back and pop your ulti in distress.

Remember if enemy's on your lane focusing on your turrets then you got a problem, they know how to fight you so make them pay with rockets.

In late game turrets are squishy. But if you have to fall back from lane push put two turrets pop ulti and you will buy few seconds or even more.

Ah and be creative with them.

Yes.. That's your main weapon. High damage ,hitting multiple targets, great range, even slow.
But !
Rockets hitting 3 or 5 (with ulti) nearest enemy's so you have to learn how to count to three.
If you can make it so you can do much damage. Don't worry if your rockets will fly off to some creeps instead of delivering deadly blow to enemy champ. it just happens get used to it.

In early game its good harass tool mana costly but you can harass, protect your turret's and do little farming at the same time. Enemy's will be quickly pushed and tower hug will begin (you can get ppls near tower too just look at rockets icon.

In mid game (lvl 8 for you) you can do alot of damage with it pushing the lane and harass like no other and farming while doing those things.

Late game.. as someone written before me you will shoot Powerful Rockets of DOOM great damage,slow and hitting multiple targets is there something more fun ? :D

This skill is little hard to use and you need to get come practice hitting moving is not easy thing but in time you will learn how to attack defense farm and scout with those grenades.

You have to take it on lvl 8 its vital. Grenade Stuns blinds inflict high aoe damage even slow... but its slow as well. Good players will avoid it mostly.

How to attack .. just throw it at the champ/creeps according to its movement try to hit in case of creeps throw it between melee and mages for maximum damage.
Defense ? if some Trynda follow you just wait and throw at his face. Its possible to stop most champs along the way to you or when they shooting but it will take some practice.

Heimer ultimate.... I think its not so important good for mid and late game as aid when you rocket and nade things also for turrets slow ability and cooldown's ofc.

As spells i take weakness and flash. That make you insane defender. and even better disabler.

At the begin Take turret and go for tear then go to mid. Wait for creeps if you are not on mid throw turret in bushes maybe you scout and do some harass. Put turret between your creeps hit different targets than your turrets and avoid fighting with champs. On lvl 2 get rockets start harass,pushing get more turrets and rockets harass and push more but be carefull for ganks stay close to turrets and fall back if you must. Now most important thing on lvl 8 you should have tear and ionian boots and grenade. Recharge your mp, get blue and push/harass like there's no tomorrow with blue you can push anyone even 2 or 3 champs will fail to hold or gank you. place turrets spam rockets/grenades push tower. If you fail go to defensive and wait for new blue then do it again. when turret on lane is down go push other lanes or go for teamfights. Put turrets in the middle on tram fight fall back a little and spam with grenades and rockets with popped ultimate. If you doing it well effects should be stunning. Late you should be able to take much hp in little time hardcore chasers or tanks may be a problem but remember you are only support not AP carry : D

Heimerdinger is great champion if lead correctly, you enemy's will hate you so much that's for sure.

I think that was all ...

Comment , Rate you can also give me a cake.

Good Hunting.

Ah and your passive makes you hard to harass and can heal turrets on lanes.