When you're facing a Heimerdinger or some other and every time you go up to get CS you get chunked quite a bit and you can't do much. The enemy laner manages to keep a decent CS while at it too. How do you manage to get CS?
Do you just build defensively? Lots of pots?
Edit: forgot to add, even csing underturret isn't possible without getting harassed
One of the most valuable assets to a player in LoL is learning how to farm under turret at all points of the game (especially in the early levels). Farming under turret is the best way to avoid dealing with lane bullies and your jungle should be able to gank your opponent easily if theyre constantly shoving the wave. This is only really not the case if youre facing a 
since trying to gank a heimer with a turret fort set up is damn near suicide. Its also worth noting that when youre not farming under turret you shouldn't be attacking minions except to kill them, but this has more to do with wave management which you can find videos about on youtube.
Also, if you think youll be in a lane in which youll be getting harassed a lot, its important to choose the right starting items. Examples include:
+ 
+
+
These starting item setups will give you a lot of sustain in lane to farm through harass.
Learn to farm under turret and apply it, that's really the best advice anyone can give though.
Decide which is worth more--the gold from farm or extra health. If you're pretty healthy and you can dodge the poke, then go for CS. If you're healthy but you're not sure you can dodge the poke, then be careful. If you're low, just back off unless you have sustain.
Play 
You're so used to getting shit on when you're trying to farm early that eventually you will learn how to farm through harassment on any champ.
Watch for when they cast their spells. If they have recently cast their spells, you can't get chunked down if they are on cooldown (heimer's turrets have cooldown as well.)
Easy just dodge Heim's harass and continue to farm or harass back.
I think a lot of it depends on what champ you are playing, and what champs they are playing. Its hard to give a blanket advice for all champs, in this situation.
Against heirmidinger, try to avoid that first big turret shot. It is dodge-able, so if you are a melee champ, get early boots at least. If your still having trouble, just go for your MR item.
Use your ability's but it all depends on the champ so if your not a caster then farm under turret.
Against a you can counter him with 
from mid-game onwards. Let me explain how, because is NOT a « beginner » Champion, and you will fail if you try to first-time without doing some proper home-work before using him as a counter.
should have a Rune/Mastery set-up that is full of Magic-Resist and perhaps even some combination of mana-regen. 09/21/00 masteries are what I personally use, and now that I look at my Rune-Set, I could & probably should re-adjust it a bit for more M-R.
I used to start with 
or on but find that it's actually always better to have a start with or just depending on how much mana you plan to use versus how well-practiced you are at avoiding or negating or mitigating harass.
should farm until he has 900g then find an opportunity to clear wave in order to base for a 
(you can do this more easily with 
but if you're not packing then at least stay in lane until you can clear a wave that has a cannon-minion in it since any waves that are pushed after that will do less damages to your turret if you cannot make it back immediately). Eventually you will want 
for your core items and by then you'll be able to not only 1v1 easily but should have won your lane & gotten the turret by the time you have (even if you haven't finished yet). You are guaranteed to have won your lane by the time you get a (normally the 2nd or 3rd item depending on how soon you want a but OR 
should always be your first item [only get if the enemy team has annoying healers/tanks like 
) unless either you or your team has been making a lot of careless early mistakes.
Beware of picking & even more wary of when/how to use the ult if they have picks like 
[when he's triggered his E] 
or you're going to have a very bad day due to your ult always getting interrupted solely because they CC you merely for auto-attacking you). -stun can be semi-countered by intentionally letting him stun you right before you use the ult. Congratulations. You now know most of what you need to know to be able to counter with ease & consistency (with anyway).
Source : just happens to be one of my main (out of 3) champions.
Let them push and ping for ganks.
It's matchup dependant. Different kits, different tactics.
