I know that there are a lot of people out there that talk about over-committing and how they just have too much to do and that we should all learn how to say "NO!" but I try not to say it. It's true. I try not to say no, especially when someone asks me to do something. I figure that if someone is actually taking the time to ask me specifically then they really want me to do it. Now, if it's something I completely don't want to do, I will go pray about it and get back to them, sometimes with a no, just depends on what God says.
The other thing I try not to do is volunteer for things, especially leadership roles. I'm a part of an active committee at church and I talk with a lot of people about a lot of different things, so I have the opportunity to volunteer for a lot of stuff. But I don't, I feel like the restraint of saying yes in open volunteer settings leaves me time to do the things that people really want me to do and I'm not stuck in things I thought sounded cool, but turn out to be a drag and I can't complain because I volunteered for it. Not that I would complain, but yeah, I probably would. I have a tendency to blame the world for my misery and suffering when things don't turn out as awesome as I've imagined them.
And that's how I help manage my time, I wait for people to ask me to do things and then say yes. It's actually quite a simple thing, but it works well for me.
What do you do to make sure you aren't over-committed?