Try to do a small corporate website. Think of a imaginary company and just start developing the site. First, make all the basic functionality - Insert some data, Select and Update that data and finally delete it. For ex. - make a db and tables for the 'about us' page and a catalog with products (thumbnail image and a big image) and info for the products. This way you will learn how to connect to the db, exec queries, upload files, pagination, extract and display data with php. These are the basics I think you need to learn before starting something more difficult.