Max out your history levels

[Nick Gioia]

Here's a good tip. Go into your preference settings and max out your history from 100 levels to 300 levels so that if you ever get too far into a project you can always go back further than just 100 levels.

[kglad]

a better tip is:

save your fla frequently with increasing version number appended and/or maybe even appending the date/time.  this is far superior to relying on undos to return to a previous version. 

if you fail to save with different file names, and your fla becomes corrupted, it is likely unfixable and returning a working version is likely impossible.  ie, all your work will be lost.