Ah yes. gather around youngins and ol' jumpoff will give you a little lesson:
That last video posted by Alex was ok...that kid doesn't really know what he's talking about...but it was ok.
Despite his "advice" not to throw your hands forward, there are actually a few different styles for front tuck set-ups that can be utilized:
*the most common set you'll see is (what I know as an 'american set') is that where you bring your arms up behind your head on the set, and throw them forward and out upon leaving the ground. You see this most commonly in all front flips. It helps create upward and directional rotation, and allows you to grab your legs and tuck. As seen here:
http://uk.youtube.com/watch?v=6u_0CLNxR3g*another type of set is called the "Russian set" which is what that kid is doing in his video. The theory is to generate alot of potential centripetal force prior to taking off, so that you rotate quickly. As seen here:
http://www.youtube.com/watch?v=jTN2g4diQ0I*the final set type (although Im having trouble finding any videos on it) is the "chinese set," where your hands actually come from your stomach area, and shoot up and out on the take off.
Of the three, I like to do the regular and russian take offs. I find the chinese one weird, and hard to generate any real power from it.
Just play around with them...find what's best for you.
However, don't forget another important aspect to having good front tucks; and that is BLOCKING:
http://www.youtube.com/watch?v=bsg1Xak07jIthink triangles
good luck