ASP.Net Design Tip #1 - Separation of Logic and Presentation

While I don't consider myself an ASP.Net guru by any stretch, I was recently asked if I'd help ITT round out content on ASP.Net best/worst practice. So, I hope this first post isn't too elementary (or repetitive), but I feel that it can always stand being reiterated. Good design practice dictates that one should always seperate presentation from logic, and ASP.Net is no different.