Sometimes, even though I know something will help me to feel better, that isn't enough.
For example, exercise. I know that it will put me in a better mood, help me get physicially stronger, etc. However, none of that seems to matter once I sit down on the couch to "relax".
So I've devised a little extra motivation: for every time I work out, I earn $2 toward my clothes/other fun things budget. It's not much, but it's a little bonus to get me moving. I'm hoping I can eventually get into enough of a routine that I don't need it, but for now it's what works for me.