I'd just let him write tons of code. Let him drive in everything you guys do, and just be available to answer questions.
Believe it or not, after a few months of writings tons of crappy code, he'll start to get the idea and start writing better programs. At that point, you can get bogged down in details (memory, etc), and also talk about general design principles.
I've heard that what separates the great artists from the mediocre ones, is that every time they practice, they improve on something, no matter how small. Let your brother practice, and he'll improve every time he sits down at the keyboard.
Edit: [Justin Standard]
Esteban, this reminds me of a recent coding horror post, and I do think you are right. But I think its still worthwhile to find methods to guide his practice. No question, I want him writing as much code as he knows how to do. Thats one reason I'm asking for sample projects.