Hm.. well I would clip them as they get long and pointy again! If he gets squirmy for the nail trimming you may need to wrap him in a towel and pull one foot out at a time to clip.

I have a lot of experience trimming dog nails (I'm a groomer) but I don't know if the quick in an iguana nail will look the same as a doggy nail. Ig nails are black, so you can't see the quick through the side. What you do is clip just a little bit until you see a black dot in the middle of the nail.. that is the beginning of the quick, and don't cut anymore lest you make him bleed. If you do make him bleed, just have some normal flour ready and take a pinch and press it on the bleeding nail. It will help bleeding stop.