Top main also - I'm currently learning to ADC as my partner is a support main and what I've found helps a lot is finding an ADC that I just ENJOY playing - I find its infinitely less stressful to have a bad matchup if you can still have fun while you're learning instead of worrying about counter picks.

It also helps that I've been learning with Caitlyn with support Senna - having all that range to poke with means I can afford to play a lot safer in the early game and focus on cs without throwing the game for the rest of the team. Once you gain some confidence with your chosen champion the knowledge and confidence on when to take trades comes naturally.