I blocked my first quilt just a few weeks ago. It is a wall hanging that I really thread painted the center on...made it kind torque weird in the middle. I laid it on the towels on the floor and squared it up with a T-square (lots of pins) then I put heavy, wet towels on top of it to press out the bubble with their weight. I left the wet towels on over night, removed them and left the quilt there to dry for a couple of days. When it was dry, I unpinned it from the floor, cut it round and put the binding on. I would block a quilt before I put the binding on, but I suppose you could do it after the binding was on.
Karen McTavish explains how she blocks her quilts in one of her books...don't remember the name of the book and it's in WA...I'm in FL now, sorry!!! The pictures she shows really helped me understand the process!