It depends on the location. I wouldn't wait anymore than a month or so before you would like to leave. Most places drop as time (within reason, of course) as time goes on- up until a certain point and then they increase. You can track the prices and if they start to go up you could go ahead and book it.
I've heard it's best to fly on Tuesdays but I haven't really found it to be that much of a difference.
I typically fly on Sundays which don't seem to bad. I'd avoid Mondays, Fridays and Saturdays.
www.sidestep.com is great for tracking fares. It includes most major airlines except for Southwest. Southwest only sells on their own website.
Good luck!
ETA: Typically flying (especially if you book at the right time) is cheaper than driving, especially just for one person. With driving you have to take a lot of things into account: renting the car, gas, tolls, (depending on how far) hotels, food, TIME, etc.