I need to improve my programming skills in order to achieve better scalability for the software I'm working on. Purpose is to learn the rules of adding new modules and features, so when it comes to maintaining existing ones there is some concept.

So, I'm looking for a good book, tutorial or websites where I can continue to read about this.

Currently, what I know and what I do is:

1. to design relational database(3NF),
2. make separate class for each table
3. put that in MVC
4. implement modular programming
5. ...write code and hope for the best...

I presume that next things I need to learn more deeply are:

1. programming codex(naming, commenting, conventions...),
2. organize functions
3. building interfaces
4. organizing custom made libraries,
5. organizing API that I'm using,
6. documenting,
7. team work...
8. ...

At last what my job is, it does't need to affect your answer, PHP CodeIgniter developer.