Hi Cindy, you have a good start but you'll want keep current on HTML standards and start doing as much digging as you can online to find as much valid information you can about the way Google functions. It's also good to learn a bit about how people interact with web pages and search results. Honestly, I would say just read, read, read as much as you can.
Remember that
SEO is comprised of 100+ factors - some on-site, some off - and Google is constantly updating the way it calculates search returns. So if you're really serious about becoming an expert in
SEO you'll want to devote plenty of time each day to getting current and keeping up.
I would recommend starting with Matt Cutts' blog [run a Google search for him - he's also on Twitter and well worth following] and branching out from there as you encounter new information!
Good luck and feel free to post back to this section for discussion on what you've learned! After all, I have to stay current too, LOL