"Dialectical Bootstrapping" is a simple procedure that may improve your estimates. This is how it works:

1. Estimate the number in whatever manner you usually would estimate. Write that down.
2. Assume your first estimate is off the mark.
3. Think about a few reasons why that could be. Which assumptions and considerations could have been wrong?
4. What do these new considerations imply? Was the first estimate rather too high or too low?
5. Based on this new perspective, make a second, alternative estimate.

Herzog and Hertwig find that average of the two estimates (in a historical-date estimating task) is more accurate than the first estimate, (Edit: or the average of two estimates without the "assume you're wrong" manipulation). To put the finding in a OB/LW-centric manner, this procedure (sometimes, partially) avoids Cached Thoughts.