At a basic level, you probably know that building materials are stronger in certain axes than others. While you could learn all about moments of inertia and beam bending, what the average DIY builder really needs is an intuitive sense of the practical ways you can configure whatever you're building with to make it stronger. Whether you're building a tank or a table, understanding the forces at work will help make it both light and strong.
Recently, I built a kitchen table for a couple in NYC using thin metal for the main support. Here are a few simple tricks for adding strength without adding much weight.