Here's in my opinion the best way to lube a cube, with maximum effect:
1) Dissamble and clean the cube, if necessary
2) Lay out the pieces, with one non-stickered side facing up.
3) Spray the pieces ONCE from about a foot away.
4) Wait around 4 hours
5) Flip over the edges, and spray them again
6) Wait around 4 hours again
7) Assemble the cube, and play with it for a few hours, to let the lube spread out
8) Dissamble the cube, and let the lube dry overnight
9) Assemble
Note: Note that in this process, you do NOT lube the core. Doing so can cause the cube to be too "sliperry"
The whole process can take a while, usually around a day for me, but it is easily worth it in the end, especially on a good quality cube with good quality lube. I know of many sub-25 cubers who use this way, and one sub-15 cuber.
-Alexei