@Martin
Experience is hard to replace, so just toss yourself into it.
Apart from that ...
Always understand what you code. Too many just do a copy-paste without really knowing, and it only takes one weak link to bla bla bla.
Don't make it harder on yourself, so use clever and easy to understand names. As a project grows, you cant keep track of what you coded weeks ago, unless you can read it from the property- or method names. That is one of the reasons why I like cocos2D and chipmunk. They are easy to understand, flexible and powerful.
That is also why I tend to avoid a lot of other tools and wrappers. Most often I learn from them, and write my own implementations.
There are a lot of other coding paradigms I find important, but that would require me to write a book on the subject :)
