Having created LAMP programs, you can branch out in a variety of ways. You can try one of the other P's in LAMP: Python or Perl. I like Python, myself. You can learn client-side scripting, or more on the server side with Java, or Ruby on Rails. You can learn to coordinate with other sites, and how to run advertisements. Every new language or tool you learn makes you stronger on the underlying fundimentals. And of course, you have more options in choosing the right tool for a job.
By now you have the meta-technique down: Google the "learning" pages or a "tutorial."
Above all, have fun, and eat the elephant one bite at a time.