Allaboutdrawing.com once sent me news letter about practicing our right (creativity) brain.
Then, i followed the suggestion.
These are the suggestion:
1. Draw your other hand. Don't look at your paper, just do a blind drawing. (number 2 on my drawing page)
2. Or, you can try doing an upside down drawing. Both of these exercises force your left brain to stop thinking. (number 1 on my drawing page, and i must confess that this was the hardest one)
3. Try drawing evenly spaced vertical, horizontal and diagonal lines. Then, practice cross-hatching by drawing all of these lines together in one square.
4. Do an outline drawing of anything near you. It can be as small as you like. Once you focus on the outline, all manner of thinking should disappear.
have a try!