If you are in bots, practice with no masteries or runes and no item. once you get good at this, you will find it a lot easier when you have to deal with your lane opponent as well.
I lot of it just comes down to learning the lane mechanics. How to freeze, when to push, that kind of thing. ADC is one of the hardest because you have to deal with 2 lane opponents as well. Positioning, balancing harass and farm, skills, its actually all very complicated.
Work on your mechanics (animation cancelling, Stop command, attack move) in the bot games with no items until you can orb walk like a pro and not miss any (many?) minions. Then you will find you are a lot more comfortable when it comes to the real thing.