If you can get a piece of rubble that is big enough that it wont be move by your tanks flow.
Dry off the spot on the rubble that you are going to glue the frag to. I actually like to take my dremel and make a little indention int he rock a little bigger than the base of the frag and then dry it off.
Put a healthy glob of super glue gel on the dry spot
Then dob off the base of the coral that is going to be glued.....i usually just lightly tap it on a towel.......or my shirt or pants.
Then stick the frag in the glue upright and let it sit on the counter for a few minutes.
then put it in tank...done.
All of these steps are not necessary as you get better at it. But follow those directions until you get the hang of it.

happy fragging