How can I avoid bad teammates?

You can't. Riot gives them to you constantly.

You can't. Try to duo queue.

Easily, just ignore them in your games and focus on your own mechanics and macro play. Overtime you'll improve in skill and just carry those bad teammates. Otherwise your just having selective memory of bad teams because the brain remembers bad things more due to survival then the good teammates or ok teammates you get.

You can't its a part of the luck component of climb. All you can do is make sure you are 1/4 at least doing well consistently and pray for at least 2/5 - 3/5 each game which will give you a chance to carry and that there isnt anyone who is feeding too hard. Which honestly i think damage creep is what making low elo hard to get out when at least in previous season feeding lanes weren't the end of the world.