1. Meetups Rock!
I can not understate the value of meeting others wanting to know more about WordPress in person at a Meetup. Meetups are usually free or low cost, and offers a chance to learn about WordPress, network with others and the opportunity to contribute back to the community just by your being there! Go as often as you can!
WordCamps are the best. They are a global phenomenon: http://central.wordcamp.org/schedule/. It is concentrated learning in a weekend in the form of consecutive hour long sessions with super talented folks, and you always get a t-shirt. I have been to WordCamps in Orange County, San Diego, Phoenix and Los Angeles. I have presented at two WordCamps on BuddyPress, Domains and Hosting, and Plugin Basics. Well, today, my session on Plugin Basics that I gave at WordCamp Phoenix was put on WordPress.tv for all of the world to see:
I recommend that if you can not get to WordCamps, or even if you can, definitely check out the sessions on WordPress.tv. Especially the videos from the most recent WordCamp Phoenix.
3. Read About WordPress
Whether it be articles online, in books such as Professional WordPress: Design and Development, or listening to podcasts such as WPWatercooler, consume all you can when you can. Google is totally your friend when it comes to searching for info.
4. Get Involved
WordPress was created with the contributions of many generous developers, designers, and writers. What can you do to help? You don’t have to code, design or write; you can test, send money, teach others, or whatever floats your boat. I am doing documentation for the Theme Developer Handbook, love that stuff. Do you have a specialty that would help others? Reply here with your comments!