Watch Michael Giroux on JCA, Howl, and Java.
At the risk of sounding cliched, get involved. My experience in the last year has been extremely wonderful. Howl is the first open source project that I have been involved in. … The J2EE environment is extremely complex … you tend to focus on a very limited subset of problems and when … you open yourself to input from other developers you start to learn that there are other approaches to doing things that you hadn't thought about. So it has been a wonderful experience for me and I think that if anybody wants to truly expand their skills in the environment, getting involved in some open source project some place and trying to participate, trying to respond to questions on the various different mailing lists or forums, all of these approaches will definitely expand your skills and it causes people to actually respond to you even though you've never met face to face.