WordPress theme developers have a lot more help in 2011 compared to just a few years ago. With the publishing of the new standard themes and lots more interest in WordPress in general, there is a ton of info for you to soak up. Seek and ye shall find!
If you’re just starting to develop your own themes, get a good understanding of the Twenty Ten theme created by the WordPress team. You’ll learn a lot about how to put together your own theme by studying this standard theme that’s included when you download WordPress.
One of the advancements in WordPress 3.0 was the introduction of menus. To learn a bit about using the menus in your own theme, get a handle on how they’re used in the Twenty Ten theme. A great menu intro by Justin will start you on your way to understanding menus.
If you’re lost and don’t know where to start, look to the WordPress codex for help in getting started in developing themes for WordPress.