Here are my tips:
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Farming, especially in the first 10-15 minutes of the game, is extremely important on ADC. Make sure you can nab that cs almost perfectly.
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In teamfights your mentality should be to auto as much as possible from a point of maximum safety. Stand next to you support/mid-laner/jungler or whoever should be peeling for you. Only attack enemy squishies if it is safe for you to do so. It is NOT your job to dive the enemy back-line. Just auto the safest target you can hit as much as possible.
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Bot-lane meta is hyper-aggression at the moment. Since it is a 2v2 lane, gold disparities can be twice as large and losing lanes can snowball twice as hard. Once you've mastered CSing, try to start mastering trading with the enemy laners. Usually an auto + some ability when the enemy ADC comes up to CS (especially the cannon minion. Most people don't want to give up the cannon, so you can usually guarantee a few free hits when the enemy ADC goes to last-hit it) or when the enemy support walks to far forward is a good trade combo. It depends on the champion though.
If you want to improve on CS, try going into custom games and just last hit minions for the first 10 minutes and try to get 90+ (almost perfect). The more you practice, the better you'll get. ADC is a highly mechanical position, so things like orb-walking, trading, positioning, farming, only come with a lot of practice.
Also in teamfights, try and predict what the enemy threat will be, and save your escapes and try to position accordingly. For example, if enemy team has an Irelia, she will likely try to dive you. Hug your support really hard and save your flash for when she jumps on you.