It would be very hard and dangerous to clip a gerbils nails I think, what with all their moving about and stuff. Plus there could be a part that shouldn't be clipped, not sure.
Anyway, put a plain, unpainted terracotta plantpot in their home as many gerbils will use it to shorten their nails on. My gerbils nails were getting long, and I read the terrcotta trick and it worked perfectly.
I've clipped nails on elderly hamsters before. It's definitely a two person job. We would usually do one paw, let the hamster play, do another paw, etc.
If you look up clipping nails in other pets such as rabbits, you should easily find diagrams of where to cut. There is a blood vessel in the area nearest to the paw called the quick. Don't cut too close to it. That's really all there is to it.
Good luck, gerbils seem more squirmy than my old Syrians.
i took my gerbil to the vet to get her nails clipped.. i had to hold her still.. only she wasnt keep on that and bit me for the first time ever.. the nurse gave up in the end and they werent bad anyway. gerbil's nails are meant to be long anyway and as david said the pot will keep their nails short enough or an empty coconut shell.