The first two tips touched on the cheapest and most expensive ways to get into macro photography: using a camera's built-in macro mode, buying a simple macro lens filter or going all-in with a real macro lens. There's actually an in-between solution that's more expensive than a lens filter, but cheaper than a $500 macro lens. For less than $100, you can slap an extension tube onto your DSLR. And bam -- instant magnification!
Unlike a macro lens, there's no glass in an extension tube. It's a hollow cylinder designed to sit between a DSLR and a non-macro lens, presumably whatever you typically shoot with (like a telephoto or wide angle lens). The tube does exactly what its name implies: It extends the amount of space between the lens aperture and camera sensor. By doing so, an extension tube brings the focal distance much closer to the camera and increases magnification.
The increase in magnification is equal to the distance of the extension tube divided by the lens focal length [source: CambridgeinColour]. That means an extension tube will have a much more dramatic effect attached to a 35 mm lens than a 200 mm telephoto. Adding more extension tubes increases effectiveness, but stacking too much weight onto a camera will make it tricky to balance.