This is what I have learned from my loads of games played: -Out harass your opponent. If you let them harass you more than you are more than likely going to lose your lane. -If you are out harassed then you need to play very passively and just coordinate with your support for when they overextend. Most adc's will overextend when harassing and it sets up an easy kill. -When harassing only get off one hit at a time. The best time to attack is when they are attacking the creeps. Typically the adc is going to be watching the minions to get the last hit so if you can go in around when they would hit the minions then they cannot hit back.
Aside from all of that the most important thing is range. If the other person's range out does yours then you should not even try to harass it will result in you losing more health than damage you deal. That is when you need to just wait till they overextend or just call for the jungler.
***Known when to HARASS and when to play CAREFUL! If you can figure that out then you will be set.
Tricks 1. Move between each attack your champion lets loose. It lets you kite better, last hit better, and chase people better. It really makes a big deal in chasing actually, letting you get several more auto-attacks off than you normally would.
2. Auto-attack the enemy when they are going in for a last hit of their own. (if the enemy support is good they will harass you during this though)
3. If you're losing your lane, try to shove it up as much as possible quickly, then 'B' back to base. Buy an extra Doran's Sword and more potions.
4. Be wary of hitting level 2 before the enemy team. If they hit level 2 before you, they are highly likely to jump on you at that moment when you're still level 1 because: 1) They have two moves each, you have one move each 2) Ignite ticks harder when they hit level 2, 3) They just got more base stats and a bit of health recovered.
That's the main stuff I have. That and NEVER give up free harass to the enemy support (by standing up too far and things like that). Sometimes you will have to decide between getting more CS and taking a lot of damage.
It depends the champions on if you can prevent them from harrassing better. If you have a Leona or Taric as a support and you have a champion that can hit hard or hits about as hard as the other ADC, then when they harass have your Support stun them and make them either have to go back to heal or to respawn.
Also Caitlyn is a good ADC to try and learn how to be an ADC. Her Q Hits HARD, and it doesn't matter if minions get in the way a ADC getting hit by it will regret it, and she has a way to check bushes without anyone stepping inside of them or warding them. Her W(The Trap) lights up the bush for like .5-1 second. She has a slight escape using her E and her Ult has great range for being a guaranteed hit if no one blocks it for your target.
Xbox 360 GamerTag: HolyKnight22 PSN: CrimsonDivide