When I first started with Sublime, I was really lost.
A few of the things I'd have liked:
* Amazingly important: better docs on using multiple selections. This is Sublime's killer feature, and the one new things most people will never have seen before. There are a *lot* of tricks to using it, and they need to be explained. (By the way, I also think this feature is still "underdeveloped", since there are a lot of things you can't do with it yet that would make it much more powerful, but that's for another day).
* Better explanation/collection of the various plugins. I *still* have a lot of things I'd like to have work, like tags (etags), which I think a plugin exists for, but I don't have the time to find it/install it.
* Better docs on the various keyboard shortcuts Sublime offers. For example, I still don't know how to do basic things like selecting all the text inside a function, or how to jump between functions (don't know if this exists, actually). This kind of things makes coding much easier.
A few of the things I'd like as a plugin developer:
* A lot of the documentation is non-obvious, and more examples would be great.
* A lot of things completely lack documentation. For example, I have no idea how scopes work, and it seems like it's something I should get to know at some point.
* I haven't looked into this, but I think there's not that much documentation on language files.