Hey man, the best way to do it is just dive in. I couldn't read very well at all last year when I joined our school's jazz band. For a while, I was in COMPLETELY over my head. Just takes time, and a *lot* of reading. Read everything, from basslines to leadsheets and trombone etudes -- that's actually not a joke, either. Trombone parts are written in an excellent range for you to read higher bass parts and for you to familiarize yourself with the neck in all positions.
Good luck! Your teacher(s) will be a huge help. It's all just work -- don't worry about becoming a better musician to make up for the fact that you can't read very well, because learning to read well will make you a better musician!
