To make it more confusing for you, there are two ways to do this:
1) you shift into neutral and RELEASE THE CLUTCH; hit the throttle, shift to the desired gear
2) you press the clutch, hit the throttle, shift to the desired gear, release the clutch.
From what I have read and heard, the first version is the correct one as it is said to be more gentle to the transmission and if you use it on the street, it should even prolong life of your transmission. It has something to do with "synchrons". Since English isn't my first language and I'm not good at technical stuff, I don't have much data to back this up, maybe someone with more knowledge on this could provide some technical information. I have read most of the stuff on local forums.
Also, as jphughan says, forget heel & toe, my leg ached from trying that and I could never manage to do it correctly. Toe & toe is the correct way here :-)