So you're C class - seriously, hook up with some of the better guys who seem to be having fun, and do some training with them.
I'm working on my M card (geeezzzz, that's a tough nut to crack), and I got better by learning from other shooters (at matches in my case, but we have six matches most months, so it's fairly regular).
Dry fire daily - even 15 minutes will do, but I'd have a really good shooter critique my technique before getting too deep, to avoid learning the wrong stuff.
Except in winter, I have a few hours live fire every Friday, and at least one match each weekend, in addition to daily dry fire. I wish I had time and money for another live session each week... The live fire is working movement, set-ups, plate racks, shooting on the move, etc., not just standing and shooting. You need to be a member (or guest) of a decent range.
If you're accurate then a little coaching, a LOT of practice, and you'll likely rocket through B class into A. Good luck, and have fun!
Edited to add: Anyone in the Denver area who wants to train, get in touch with me.