Did you ever find yourself sobbing over the keyboard, because you ruined that beautiful image you created yesterday but which needed some touching up?
Make it a rule to NEVER work on the original graphics!! Open PSP, open your image, make a new copy of it by going to Window > Duplicate (or use shortcut Shift-D) and close the original. NOW you can start modifying.
But still: always SAVE OFTEN (preferably in the loss-less PSP-format) while you work. After you did something you like: save it. Did you really mess up: clear the image and open the last version saved, so you can go on from the moment everything was still OK.
Be sure you always work with 16 million colors: go to Colors > Increase color depth and when the option for 16 million colors is not greyed out, click it. Most of the effects and filters won't work if you are not in 16 million color mode!