What are you wanting to frag? They're all pretty different. For
SPS, you can just break off a piece, and glue it ot a new plug or rock. You want to use a gel superglue with cyanoacrylate as the active ingredient. Make sure you cover the entire bottom of the new frag so the coral does not get infected.
For
LPS, you can just break off a branch and do the same thing, make sure the bottom of the new frag is covered.
For softies, I just try to break off a part of the rock that it's on with a hammer and chisel. You can also scrape it off the rock and glue it to the new rock or plug. Make sure to dry the bottom of the coral with a towel before applying the new glue to a softie, so it will stick.