I don't have a schedule, does get their nails clipped before each mating and bucks get them trimmed when needed. I lay them on their back on my knees and use a pair of dog toenail clippers. Trim a little bit at a time so you don't take off too big a chunk. The dog toenail clippers work for teeth too (hope I don't have to do that again anytime soon!).
I'll start clipping heavily at 3 or 4 months. Before that, I'll trim them as needed. (Babies nails can be so sharp!)
If I need to get them short quickly, then nails are trimmed once a week.
Once they're at a suitable length, once a month. Every now and then someone'll have sharp nails that I can't trim, so i'll take the time to file them down.
Once a month for the big rabbits, and twice a month for the Mini Rex, because their nails grow freakishly fast. I also do touch ups before matings and shows.
Mine get clipped when ever they need it. Since they are angoras and handled a lot their nails are checked all the time.
I use plain old human nail clippers. Rabbits dont have large, hard nails like a dog. They are soft and sideways flat enough for just people nail clippers. I just use the clippers sideways to match the flat on the nail. Never had a prob either clipping nails.