The way I do islands is to make a symetrical lattice and copy/paste many copies of it. One large one for the beach, the next one for the next level of shore, then the next one for the next level, etc. Add other lattices for hills/mountain, or large rocks. Put trees with small leaves within the layers of lattices or rocks to make it look like wild vegitation. Of course the palm trees Bryce has and what can be found in the freebie section here at RD are handy. I would also sometimes take a rock or lattice and copy it, paste it right over but making it slightly larger, and put one of the semi-transparent type vegitation materials so that the lattice/rock would look like it has vegitation/growth on it. And then I like to dress up a water scene with rocks along the shoreline.

The best way to learn to do islands is to do what The Bryster has mentioned... to look at the gallery. That's what I did. It took me a long while and I have several versions of islands in my computer, but posted only a few here. All my islands I started with Bryce 5, and had to make some of my own materials. With Bryce 6, there's a lot of good materials that comes with it, one or two looks kinda like my own mats. They aren't that easy to do, especially the shore.

Hope that helps to get ya started!