Used to be able to do it in 50 seconds, now it's more like 1:30 minutes.
To solve it first time, think of how you can "scramble" certain blocks without messing up what you've already done. The process usually involves moving 2 blocks of the cube away from an incompleted plane, and then moving those two blocks back from another orientation, resulting all the other incompleted blocks to be "scrambled" around. Observe the pattern and you can gradually move specific blocks to where you want them to go.
When you get more advanced for speed, you start thinking about removing redundant moves.
The 4x4x4 Rubik's Revenge was much more frustrating!