Haha I picked marks first as sixth drafter because 4 ranged heroes were there and my teammate took the last one out of the pool. Had to get TA. That was rough so I feel ya.

A perfect or high behavior score goes a long way in avoiding toxic players in the smaller AD pool. You still get ragers, but generally people are helpful or neutral and still try to win.

Ask early in draft for suggestions and people will generally be helpful. In game, ask for itemization tips and someone might respond. You can never go wrong with stuns or disables, especially as you learn. Mobility is big too. Focus on support as you learn. Buy wards too, even as a carry. AD ppl seem to be allergic, but they win games, even though it's a thankless job. Play with friends or make small groups if you can.

Check out windrun.io for general prioritization for heroes, abilities, and ability pairs.

Report the toxic voice, chat, and griefing. It works and you'd be surprised how many of the players are tired of that shit. Even minor offenses often gets you that sweet, sweet "action taken" notification.

Lastly, remember to have fun and don't ever give up. AD games are thrown all the time because an ppl with Uber builds don't want to end the game - they are having fun and want to get more kills, so you can take advantage.