In a nutshell…“write about programming.”
Longer version (the quote comes from an interview Dave did with The Code Project):
“What advice would you offer to an up-and-coming programmer?
Write about programming. Start a blog, answer questions on The Code Project or Stack Overflow, or whatever else suits you, but find some way to write about programming.
I can’t count how many times I began writing about something I thought I knew thoroughly, only to find that I had to fill in several important gaps in my knowledge to write about it competently. Just as important, you have to learn topics more comprehensively to distill and teach them in simple terms. The combination of writing about programming and making that writing as clear and simple as you can is a powerful exercise.”