Miffys claws are all white so I have been cutting them myself since I got her, But when i take her in for her jabs every 6months I usually get the vet to take a bit off just to save me the hassle. I had a guinea pig as a kid with 3 white feet with white nails and 1 black foot with black nails, I used to do all the white ones, then judge where abouts I could cut on the black ones + a little extra just to be safe.
To cut Miffys nails I usually get someone else to pin her to the table 1 hand over the rump and 1 over the ears. I have also found that since 1 of my vets did this in front of me, that its a little easier to pull the back legs behind them and then trim all the nails as u can get to them better.