By the sounds of it your beyond tutorials now and it's time to start developing your own ideas. eBooks are boring and long where you do too much reading and not enough hands on coding. Pick something you need and have a real interest in and code it.
A twitter plugin using their api, facebook plugin, link checker, a post generator, guests message script, etc are some types of examples.
The next step is to research what's existing, how their built. Dy-sect them. See what's good, what's bad, what type of security they have, which have features and how do the features work. From this you'll get a great understanding and learn new things.
Then as you code your own to your own needs you'll encounter problems, Google them and if you can't find them ask questions and get help in forums and coding areas.
Once you get it coded and working you'll start adding features and settings to it.
After a while you'll have another idea of something to code which is slightly bigger and more complex and you'll redo a similar path again learning new ways of doing things and more advanced and techniques. It's just sorta a natural learning cycle.
