In principle this exercise is very simple to conduct. Key to get intensity in is to apply sufficient force to your base with your clamping hand (as it is with all other girth exercises). Thus, as I suspect, the problem most PErs have who don't get much expansion out of it is, that you don't or can't clamp off your base tight enough.
Other than that, many questions concerning the [words=http://www.mattersofsize.com/forum/penis-enlargement-forum/12539-slow-squash-jelq-nothing-give-me-better-expansion.html]
SSJ[/words] address secondary aspects of it which can be varied to regulate intensity: such is whether you clamp off at your very base and stay there or move up an inch, if you should start with 80 or 100% EQ or if you should move around your dick with your heel or not. Use your knowledge about blood flow mechanics and common sense here: if your intensity is too low or your erections vanishes too fast, start with 100% erection and spare any bending movement (for it accelerates the blood reflux) and just push down with your heel straight (like crushing a coke can as someone said here in colorful comparison) and/or push down harder with the upper hand. If your erection begins to subside (which it inevitably will in the course of the conduction) then you can loosen your clamping grip for a split second and kegel hard to get blood in again and/or move up an inch with your clamping hand. Otherwise (in case you already have good expansion at that point) you can begin to bend and move around your penis to punctually aim at different areas.
And if your hands are just too weak to get the job done and all these modifications fail, get a clamp or at least a tight
cock ring as a substitute for your base hand.
To sum things up: there are a lot of possible variations of performing this exercise which are all "correct". It depends on your specific situation-related needs which one is to prefer.