If you want to get on Super Yachts STCW 95 is your ticket. It's best to go through a school where you can meet people in the same situation as yourself and possibly get some industry contacts through former students. I did UKSA in Cowes and it was very good. The next step after that is to sign on with a crew agency (Bluewater is the standard one) and get yourself to Antibes and start dockwalking. Some agencies offer crew houses for job seekers but other people just rent a flat with other people in the industry. Most of my STCW class found day work quite quickly and most of that led to more full time jobs.
Another route you might want to take is working for a charter company as a hostess. In my opinion Navigare is the best, but there are others. For a cost you can do their "hostess school" which is like a cooking, sailing, cleaning boot camp, but if you pass, you have a job with almost any charter outfit. Hostesses work very hard though. Navigare has bases in Greece, Croatia, Turkey, Sweden, the BVIs and Thailand. As an added bonus, if you're young and fun, Navigare works closely with The Yacht Week, which will hire hostesses for the summer and is the job of a lifetime. The Yacht Week also does a hostess school closely modelled on Navigare's program.
Here's a link to The Yacht Week official trailer. They are other videos to check out on their website too.
Best of luck
Here's their trailer