>> For those of you who have already done this or are
>> in the process, what would you do differently and
>> what is your advice for someone who is just starting?

0. Arrange some free (non-paying) time in your work schedule
1. Choose a real-world application for your sandbox.
2. Choose a specific solution domain, i.e. Web App, winform app, web service
3. Browse your bookstore and find a good book that covers your solution domain
4. Choose either C# or VB.NET and focus
5. Google is your friend.

Good luck!