I've run a half, my wife has run several half and full marathons.
A typical training schedule has you slowly build up to the full distance over the course of three months. Typically you'll have three "short" runs a week, each of which are about 1/3 the distance of your long run. So, for example, the first week would be 1 mile, 1.5 miles, 1 mile, and then 3 miles. Use the short runs to work on your speed, but don't run too fast on the long runs. Always start out slow--your last mile should be your fastest.
You'll hit your longest training distance (13 miles if you're doing a half) about 2 to 3 weeks before the actual event, so your body has a couple of weeks to recuperate.
When it's the week of your event, you should:
Carb-load (eat plent of carbohydrate-heavy foods) throughout the week and especially the day before.
Make sure to keep your legs active after the event. If you hop right on a plane, for example, potentially fatal blood clots can form in your legs. After the event you need to keep moving, so I suggest you go out to a club and go dancing.