1. Make a physical model.
2. Draw a graph.
3. Draw a picture (somewhere in between 1 and 2).
4. Organize data in a table or chart.
5. Look for a pattern (visual or in data).
6. Work backwards from the solution, if you know it.
7. Solve a special case or related simpler problem first.
8. Divide the problem into cases.
9. Argue by contradiction.
10. Estimate, and then refine your guesses.