Some time ago, I some problems with my old character - a game of play-by-post went into a really long hiatus, and by the time we had continued it, I have long forgot pretty much everything about my character, except for the basic class-gender-name. And it's not that fun to play just a class, as far as I can see 8)
It took some time to figure out what to do, but in the end it looked something like this:
Read your character's pre-adventuring biography. If you've got the basic idea what you were doing before, just reading some facts from character's life may be able to help you remember how you had played and what was fun.
If it did not help, you could always re-read the old adventure. Play-by-post is a wonderful thing for this situation since as long as your old post were not wiped out, you will be able read it now, tomorrow, or ten years later.
Steps 1 and 2 should be enough for you to create something like a "behaviour matrix" for your character - you will be able to quickly realise what he/she will do in the exact situation, and you are most probably will be able to remember what was fun about the character. Through, if that "fun" is not as much fun anymore, there is a way around that
Tweak your character. No, I'm not talking about changing some class features/spell selection and such. I'm talking about making your character more complex. Give him/her some phobias (like, being afraid of spiders), quirks (constantly nibbling one's own nails, collecting raisins, or perhaps always leaving a gold coin in a fountain), likes and dislikes (a barbarian who refuses to eat his veggies, especially carrots, sounds pretty funny - and interesting. So does a monk who has a drinking problem, and starts to act as a cliche PALADIN if he is drunk) - give your character some minor to mild traits that may, or may not technically hinder him/her during adventure. The perfect way of doing that is to bring up something what was never on the table
Like, facing a problem of dealing with some circus people, the party asks their bard to do the talking... Which he is suddenly incapable of doing because he is froze in sheer awe of clowns - turns out, he goes all fan-geeky over clowns because he simply loves those frilly guys since he was a kid. So, the party has to deal with it somehow first - like, to get the clowns out of their bard's sight, or letting somebody else to do the talking, or doing something else to solve this problem. This situation brings some roleplaying fun to the table, lets you bring up some more layers of the bard's personality and, besides somewhat prolonging the session (which is not that much of a problem in play-by-post), it's a win for everyone
Think of those tweaks as of "junior flaws", which instead of feats bring more RP to the table. Make your character not perfect - and if he/she already is not - push that "perfect" away even further. Sky is the limit - or maybe the bottom is, depending on you 8)