Recently I tried to learn how to play a champion that I hadn't played before (Rengar, but I'm not looking for advice on him specifically). I loaded up some bot games, and went 10-0, 11-0, then 15-0. I decided it was time to try a normal blind pick. I went 0-8, and my team spent the entire time saying "gg Rengar noob" and "report Rengar for feeding." This has happened literally every time I've tried to pick up a new champion. I learn eventually, after feeding like crazy for a few games (I'm getting decent at Rengar now). But the whole time, I feel like I'm letting my team down and ruining other people's experiences.
So how do YOU learn a new champion? I'm not looking for advice on any champion in particular, just how do you go about doing it? I can dominate intermediate bots on virtually any champion, but those skills just don't translate to being able to take on players. Any tricks or tips would be appreciated, so I can stop being a "feeder noob" every time I try to pick up somebody new!
TL;DR: other than bot games, what do you do to learn new champions?