Hm, not the easiest thing to answer... but I'll try to!
Apathy isn't something I've really conquered yet, but it just sort of comes and goes. I haven't found any solid source of inspiration really, but I'm compelled by obligations and things I have to do in order to keep things going, and to help those whom I care about. It's usually easier for me to be more committed to something when it involves someone else than just myself in the matter, but then again, I tend not to really get involved unless I get to know people (which is kind of contradictory).
For me personally, apathy and interest come and go both in larger trends and smaller ones. I'll have periods of ups and downs, but even little things can make or break my day sometimes. Some days some random act of awesomeness just brightens things up, and on others, things I like to think of as stupid kind of ruin things. However, I've managed to stay away from drugs, alcohol, and tobacco due to having seen their effects on other people. That, and I'm also asthmatic so smoke is rather irritating to me, and alcohol just smells terrible to me... as for drugs, I value what little health, self-control, and money I have. Lol.
I think that the common theme in all my successful battles over apathy is something to look forward to. No matter how small, it can drive me or sort of lead me along until I find something else. Also, friends are another great resource: I often find doing nothing with (true) friends is more fun than doing something alone--for the most part.
'Hope this kind of helps? Lol.