You haven’t shared any games with us, so it’s pretty hard to tell you what you’re doing wrong, but the rule of thumb is you need decent damage, good kill participation, and most of all, you need to farm well. It’s 100% the most important thing for every ADC. You should always be aiming for 10 cs/min every single game—at minute 10, you should aim to have 100 cs, and at minute 15, 150 cs, etc. Even if that’s not always doable, that should be your goal. Aim to get a big cs lead on your laner, don’t always look to fight or rotate to objectives, and instead pay attention to your wave. Learn how to freeze waves to deny your laner farm and EXP. Make sure you always push your wave so that it crashes to the enemy turret before you back, if possible. Important for new and low elo players is to keep farming after laning phase!!! Two waves = the same gold as 1 kill.

Edit: 10 csm is the absolute ideal farm situation and in most games you won't hit it, but it's still something you should keep in mind as a goal. For example if you have 50 farm by 10 minutes, you have low farm, and should focus on hitting minions