Linda,
Turkey is an excellent place to find a crew position. Several dozen boats will be arriving in Turkey from Indonesia in 4 - 6 months. Many of the participants in the Indonesia Rally which left Darwin 2 weeks ago will be shipping their boats from Singapore to Istanbul.
You can find most of these boats listed here:
http://www.sailindonesia.net/home/home.php
You can also follow many of these boats via their blog. Many that I know use sailblogs located here:
http://www.sailblogs.com/
One of the last stops when leaving the Med for the Caribbean are Gibraltar and the Canary Islands. The ARC Gran Canaria to St. Lucia Rally is a good place to start looking:
http://www.worldcruising.com/arc/
You are more likely to find a crew position prior to a major crossing than you will while a boat is Island hoping within the Med.
Also, once you arrive in the Americas, there is the Pacific Puddle Jump
http://www.pacificpuddlejump.com/
which many boats heading to the South Pacific take part in and a large portion of the those boats will be looking for good crew. So once you get experience crossing the Atlantic, you shouldn't have any trouble finding a ride to Tahiti or Bora Bora.
While in Bora Bora, it is easy to find a crew position from the Bora Bora Yacht club:
http://www.boraborayachtclub.net/
Most everyone is interested in a little extra help crossing the Dangerous middle to Tonga.
Once in Tonga, most boat wait several weeks to a month for a good weather window to either Opua, New Zealand or Fiji. If you find your way to Vava'u, Tonga in time for the Tonga Regatta, you shouldn't have any trouble finding a ride to either New Zealand or Fiji.
http://www.regattavavau.com/#home
Hope this info helps!
Cheers,
Ken