If you are young and want to bum around the world for a few then GO FOR IT.
1. You need an instructor rating to open most doors- teaching specialities helps.
2. PADI is a your best option for finding work. (Dont start flaming- I said best option for finding work on resorts.)
3. Liability insurance
4. The more skills the better- compressor mechanic, computer skills, boat skills, captain, outboard mechanic, scuba gear repair, etc...
5. Being a UK citizen opens doors with work permits.
6. Being good looking helps. Sadly I fall short

7. Having 100 certs helps.
8. Knowing a few different languages can be huge.
Most importantly you will need a strong work ethic and realistic ideas about resort work. Some people think working in resorts means playing in the sun and teaching diving to happy, attractive, fun, fit people. The reality is you bust your a$$ humping tanks, dealing with disgruntled customers who cannot believe the wind has the nerve to blow hard duirng their vacation, and dealing with sketchy resort managers. For me it is alot like a bartending lifestyle- you are really working more in the service industry as well as the dive industry. When it is fun it is really fun...when is sucks it really sucks.
However, I have been to parts of the world and seen cultures and sealife most people only dream about. I have also made friends with amazing people from all over the world: USA, UK, NZ, AUS, South Africa, Canada, France, etc... For me it is so worth it. Last summer I lived in huts in Fiji and the Solomon Islands. This year back to the Lesser Antilles. Next year I think I will be in the Red Sea...maybe...you get the point.