Numerous websites online offer tutorials on database designing. Some specifically detail php+Mysql usage. While there are numerous aspects of a database driven website, the two most important aspects are design and implementation. While most websites teach you how to write effective sql queries, not many teach you the art of design.

Tom Jewett form Department of Computer Engineering and Computer California State University, Long Beach has a gem of a website that talks about database design.

It it one of the best references available if you are looking to learn the fundamentals of database design or just refresh your sql skills.