Find some small thing to 'fix' first. Get the gratification of a positive result. Often when I'm confronted with a long TODO list, my eyes glaze over and nothing gets done. To get out of the funk, I do little, easy-to-do things that produce near-instant results.

Also, avoid (at first) making changes which don't change anything (eg. removing comments, rearranging routines, renaming variables to better names, etc). These may help readability, but I find they ususally aren't very inspiring. Better yet to find something which can be made more efficient or more scalable. After working on these, I feel I've accomplished something.