I usually cradle them in my left arm (I am right handed), and use both hands to hold the paws and clip the nails. Having to do it myself, I have learned to hold them and clip. A few don't like to have the nails done, so need to be wrapped in a towel so they don't squirm and kick.
Doing nail trimming for other people, some rabbits don't like being turned over, so I can do them just sitting on my lap. It's a bit more awkward since I have to move them around to get at all the feet. I pretty much just have them on my lap, and hold one foot out a bit and clip the nails.
If you have someone to help you, then can hold the rabbit and you can trim nails. There can be a few ways to hold the rabbit from facing out with the bum supported to facing in or just being held normally and you moving around them. It can be easier to have help so one can tend more fully to the rabbit and hold them so they are more comfortable.
Rabbits generally don't like their nails trimmed or being turned over, and the normal response is to try to get away. It is good to be able to turn them over so you can check their underside and do a basic health check. Getting them used to handling is also important, so try just turning them over for a short time without trimming the nails.
Nail trimming does take some practice. Don't give up, but maybe get some help if you need it.
