Besides the usual working experience, some of the following certifications will be useful:

First Aid

Offshore Survival Training

Helicopter Underwater Escape Training (HUET)

Not every employer needs you to have all of these certificates, and those who require them may offer you training when you are hired. On the other hand, having these 3 certifications certainly gives you a leg up when HR looks at your resume.

Even if your company doesn't force you to take these courses, you may want to pay your own way, especially the Offshore Survival and Helicopter Escape courses. Consider what happened recently (Feb 18, 2009) - the helicopter sending 18 Scottish oil rig workers to their oil platform crashed into the sea. Fortunately, no one was killed. Their survival training certainly saved them.

You'll work the same hours as the rest of the oil rig crew - 12 hours on, 12 hours off. Normally, once you set foot on the oil rig, you won't leave for another two weeks. After that, you get two weeks break, and then the cycle repeats itself. However, be careful to confirm this with your employer - there are cases of 4 weeks on/4 weeks off and even 6 weeks on/6 weeks off.

As a steward, you will housekeep the living areas of the oil rig and help the cook in the kitchen.