Re: [n_pertuset] Pre - Base question
You'll want a canopy in the 240ish range. You might consider something slightly smaller for skydiving (because in strong winds you might not be able to get back to the DZ), but for BASE practice, sizing right on what you'd use for BASE is best.
Your best bet is to find a local BASE jumper and get them to coach you through your skydiving with BASE in mind.
Definately work on accuracy (including cross-wind and down-wind accuracy, if your DZO/S&TA are ok with that). Also practice some riser flares (again, check with your skydiving folks to make sure they're ok with it).
Try to do some CRW. If you can convince some locals to do CRW on BASE canopies, that's a really good learning experience as far as the canopy's performance envelope. But even just "normal" CRW is really good experience, too. CRW jumpers are the only skydivers who are really used to flying in close proximity to obstacles (which is a mandatory survival skill for a BASE jumper).
Also practice tracking. Tracking well is a major plus for a BASE jumper. If you get a chance, trying out a tracking suit like the Phoenix Fly suit is both fun and educational. Depending on your skydiving experience level, you may be able to throw on a wingsuit as well, but if you're just skydiving for BASE, that's probably not going to be as easy, due to low skydive jump numbers. Be aware that the Prodigy is a very BASE friendly suit (Phoenix Fly claims to have developed it as a beginner suit, but my honest opinion is that they were really trying to build the world's best BASE tracking suit). The S-Fly Access should also be good for BASE. (Basically, you want to be able to get to your risers for heading correction without spending the half second to pull the cutaway cables.)
To repeat: Your best bet is to find an experienced local BASE jumper who can guide you through the skydiving progression. This will also set you up with a mentor for your BASE career.
Hope that helps.