In my experience, of the best ways to get started in design is to replicate other people's designs as perfectly as you can, just to get the hang of designing something good.
For example, the other day I recreated the hat icon here: http://hicksdesign.co.uk. This is mine: http://cl.ly/GYHw.
If you make one thing every day, you'll eventually be pretty good at fleshing out your own ideas.
Resources: http://pttrns.com; http://teehanlax.com/blog/iphone-4-gui-psd-retina-display; http://dribbble.com