some tips:
-pick 2-3 champions in your main role and 1-2 in your secondary that fit your playstyle and stick to them. have a flex or two ready for fiill. try to keep your pool mostly to champions that are non-high priority so your pool doesn't get pinched every game. as an ADC player most champions work kinda similar so it's not the worst to be stuck with a less familiar one if push comes to shove though
-watch high elo adc gameplay and understand how they play. xfsn is a good recommendation. lots of pros also stream.
-during lobby + loading screen go to the league wiki and read up on your enemy bot's abilities, cooldowns, damage, etc. then as you get comfortable with facing bot lane champs read up on other lanes, etc. doing this every game will help you learn the game a lot faster
-after every game, reflect on what you could have done better. at first just focus on small things but as you realize how you can do better with your micro/mechanics you'll also start thinking about your macro, itemization, etc.
-as an adc player it's a good idea to practice your CSing outside of ranked. practice tool is good but if you have time to burn norms work best as you'll practice vs real opponents and learn how to move around the map to catch farm without missing the action
-after you take bot tower you will want to either group and siege objectives or farm while there's nothing worth taking on the map. don't just keep going back bot. you only want to do this if you're the one who lost tower and the enemy bot keeps coming back with no kill pressure on you (so they're wasting their time)
-way too much to cover when it comes to teamfighting, but broadly - focus nearest target unless you know what you're doing, stay in your max range as much as possible (auto spacing), master moving between autos (kiting), track enemy threats (cooldowns, position)