The Meaning of Life, the Universe, and Everything.
If you need to build out straight in front of you, then you have to get to the edge of the blocks you're standing on, and sidle up just barely over it, to where you can see the leading face of the block you are standing on. The best way I've found to do this is to go forwards and backwards at a slightly forward angle, kinda like when you are parallel parking, until the face becomes visible. That way, you don't accidentally launch yourself into the void by stepping a little too far when you only needed a little baby step to go.
Edit: Or, if you're talking about the many blocks of dirt more than you can manage to ever possibly carry. Yeah. That totally sucks.