Like they say man. Just spam games.
It's literally that simple. Play ADC until you're use to the mind set of one.
The only way is to experience it yourself, thus spamming games = experience.
Learn about A click or X click. Basically you click the A or X key and left click the ground, your character will now attack the closest target.
There are a couple of things I do as an adc and it's kind of difficult to explain as it comes off as second nature from playing it so much.
But learning to move your character as quick as you can after an auto attack is a good place to start.
Positioning obviously.
Trading in lane.
Target priority ( people think hitting the tank is wrong, very very awkward, because this rumor is false, in fact you do the complete opposite )
More importantly, remember most things are situational, so the only way you will know what to do in situations is by getting first hand experience.