The best way I've found is to just figure out something you want to write. Something simple like adding, listing and changing something in a database.  Then get a couple of books, I like the Wrox seiries as they make great references later, get the Basic and pro versions of each for vb .net and asp .net.

Then just jump in and start writing something.  Each time you need to know how to do something look at how it's done in one of the books and moduify it till it works for you.   Use the Object browser A LOT!!  It's your friend and you will find all sorts of stuff that way.

Load up the DNN Source code and see how these guys do some things.  Leave Intellitype turned on and look through all the overloaded options availble in some methods, they sometimes give you ideas on how to do something different or better.

Don't worry a whole lot about pretty code for awhile, and make lots of comments in your code so you remember what it was you were trying to do with it later.