I sometimes feel one coming on, but relax my leg straight away which usually stops them. I count myself very lucky that I haven't had any cramps so far. But I have been wondering if it could be because I have had bad heartburn and basically live of Rennie & Tums tablets... sounds like I might have been right.
To stretch your hip area:
I used to get cramps sort of in my bum cheek. This is the best way that I know of to stretch it out, although it is not ideal and hard to explain.
Sit on the floor with both legs straight. Now take the leg where the cramp is (let's say it's the right leg) and place that foot over the other leg, resting the right foot next to your left knee (or further up if you can). Now twist your upper body to the right and with the left ellbow (opposite to the crampy side), try to push the right knee to the left side as much as you can. Hold that stretch.
I think I totally confused you now, but I can't think of a way of explaining this better.
Here is something similar, that you might want to try:
http://www.spinalhealth.net/stretching.html