When it comes to databasing, there's a lot to learn. If you haven't done it already, find a good book about database design and learn to put together a solid database - on any platform. It's an invaluable skill and it will save you plenty of time and headache in the long run. Also, learn about MySQL. It's a complex but interesting database with a wealth of useful documentation. Learn about table structure, data types, and SQL. You can actually achieve some pretty impressive stuff if you know enough SQL.

Finally, there's PHP. The PHP Web site has nearly everything you need, from a comprehensive manual to mailing-list archives to code repositories. An excellent way to learn about PHP is to study the examples used in the manual and to check out the code archives. Many of the posted scripts consist of functions or classes that you can use for free in your own scripts without having to reinvent the wheel. Additionally, the mailing list is an excellent spot to check out if you get stuck. The developers themselves read the list and there are plenty of knowledgeable people there who can help you along the way.

Good luck and good coding!