Having a strong foundation is very much essential to mastering anything in this world. This is true for PHP development as well. Master the basics and see how well you do in this area. Also, it is important to learn from experienced designers and developers. This helps you in getting insights. Know how they lay their web pages and accordingly work out.
Next, have a good vector graphics editor for yourself. This helps in gaining expertise in the designing aspect. Web designing is important because design of a website is very much important as it helps in attracting visitors. A great way to learn and master graphics design is by making images using vector graphics. You can get adobe illustrator to practice graphic designing. Another options for beginners is to get the free and open source ink space and practice on it.
One of the most crucial things to be taken care of is codes. It is a normal practice for PHP developers to copy codes from other applications and locations. Know what you are copying. The important thing to be taken care of is to know whether a copied code is compatible with your project or not. Understanding the code is most important as this will help you in troubleshooting any complexities that may arise later. Buy some books for this purpose because they are immensely beneficial.
Practice on scripts this helps in mastering PHP. You can take a script and go deeper to learn its very core. Understand the functionalities offered by the script. You can try Content Management Systems like Drupal and Joomla for working on scripts.
Lastly, after practicing all the above mentioned things, try to build websites before taking up a real project. There are various ways through which you can pick projects. There are websites that feature projects from various clients and you can bid for any project that you want. Using your own website for picking projects is also an option. Get some hosting and a domain and start creating sites for your clients.