The way I do it is to get some height, point it straight to the ground with about 1/2 throttle. After it picks up a good bit of speed, start into a aileron roll. After at least 1 or 2 rolls, jam the sticks into the top, inside corners.(full throttle, full right rudder, full down elevator, full left aileron.) The more surface deflection, the better but I recommend no more than 45 deg. in high rate for most planes. A big ole honkin' engine helps a bunch too. I have found that some planes wont blender at all, like my GP .40 size extra. I suppose not enough control surface area. The more speed you have when you enter the spin, the wilder the spin. It's sometimes followed by a flat spin and a tumble. It puts a lot of stress on the air frame, most of the stress will be right behind the wing. I have heard of more than one breaking in that spot, so I added some extra light ply gussets in my fuse. It's really just a timing move, that is very easy to do. It's sorta like doing a snap roll while diving straight to the ground. I have a H9 1/4 scale Cap that will do it very well also. Give it a try, and make sure you have plenty of surface throw. Have fun.

P.S. I'm not one of those "expert" 3-D guys but I can hammer out blenders all day long. It's only slightly harder to do than a snap roll, but is the most heart stopping maneuver you will ever see!