What kind of cart do you have? Sounds like an easy entry type?
Electric sander and rustoleum - that's what I did for mine - kept it going for over a decade. I've since up graded to a trail cart that is a little bigger and fancier (once I knew that the driving wasn't just a phase
Enlist the help of another driving friend or look up your local driving club and go watch a show. Get to know some folks and find out who they use for trainers, etc. Unless you train horses yourself, you'll want to get some help.
Some horses can be driving in 15 minutes and never make a wrong move and yet others aren't 'settled' enough to take to the cart until they are teenagers. And some of my best driving horses were teenagers when they started driving, too, I might add.
I break/train my own horses and also teach them to drive (well, the ones that have the right 'stuff between the ears' that is) and LOVE it. I currently only have one who drives right now (my half Welsh) but I've already begun ground driving and dragging things with my big 16hh foxtrotter.
He's coming along slowly - most definitely not the one who picks it up in 15 minutes - he's probably going to be the one that needs weeks and months of practice. But he is a dead broke, solid and safe animal under saddle so once he realizes the cart isn't going to eat him, we will be home free.
Lot's of patience and time. Find someone who has done this a bunch of times and enlist their help. I say start a progress blog and have some fun with it!