My dog's nails are way too long, my fault. I was always afriad to do it myself and she's too big for me to take to vet or groomer often. But I'm okay with trimming them now, so my question is how often should I trim them to get them shorter and how short is too short?

Technically, you trim them when you feel it's necessary, and it really depends on the dog. My dog (long haired chi) requires a trimming every 2 weeks or so.

You want to cut them so that you avoid the dark center in the nail, and give yourself some room. If you're uncomfortable, ask the vet next time you go and I'm sure they can show you.

How To Trim A Dog's Nails, Called a Pedicure, at ThePetCenter.com should help

If your dog has darker nails its harder to see the quick which is the dark center in the nail. Its easier however to see the quick if you look on the other side of her nails.

I had the SAME problem.. except for my dog is small, so I took her to the vet and he said they were long because I kept her inside too much, and that I should take her for a walk more often so her nails would like, scrape or something, on the side walk
But, even walking her you still have to trim them, it's kind of scary cause the dog moves a lot, but just don't trim right by the quick and it's okay!