What is the best way to practice a champ?

I play a ton but I don't feel myself growing as a player nor do I feel like I'm getting anywhere with my current main. So I would like to exchange the champs I use now for someone who feels useful in Silver 2 and higher. Right now, I use normal draft to practice but I often find that people are trolling or not really trying and I don't want to lose LP due to me trying to improve with a champion.

What's the best way to practice a new champion for ranked?

Also, if anyone knows what the best mid laners for carrying in low elo are, I would much appreciate being told so.