Daniel Solove (George Washington) makes a number of sensible points. One thing he doesn't mention, which is crucial, is to find out in advance of the job talk what the format will be! It's true that the normal format is 20-30 minutes of presentation, followed by 30-40 minutes of discussion. But confirm that with each school! Also, find out whether you should circulate a paper in advance, whether it is reasonable to expect the audience to have read a pre-circulated paper, whether the school is equipped with whatever AV needs you have for your presentation, and so on.