[WiLLiSTER]

Well, if you're really this serious, I'll try and get serious.

You want to have equal pressure like Helix said. You also don't want a lot of pressure. Putting a lot of pressure onto the die will make it harder to get a good launch off. Just practice getting it in between your hands for a while and slowly move your hands in opposite directions so you can get a feel of when and where the die is leaving your hand. Once you start getting the feel for it and get it going, you'll be able to add more pressure which will allow for longer, faster spins.