A wobbly table is one of life's little annoyances. It's an easy fix that requires only the simplest of tools. See How to Fix a Wobbly Wood Chair for more ideas.
Place the table on a hard, level surface so you can examine the source of the wobble.
Look at the leg that is causing the wobble. Some table legs have a glide, a round metal or plastic knob on their foot to protect floors against scratches. If the glide is missing, buy a replacement at a hardware store. This will fix the wobble.
If a loose joint is causing the problem, tighten any screws in the joint and secure it with wood glue. Hold the joint in place with a corner clamp while the glue dries. Or, if you don't have a clamp, wrap a length of rope tightly around the joint and another leg of the table.
If one leg is slightly shorter than the others, lengthen it. Use a tape measure to determine the length of the short leg and of one of the other legs. The difference between these two measurements is the figure you need to repair the wobble (see steps 5 through 10).
Use a sharp butcher knife to slice a wine cork so that the height of the cork is the same as the difference between the legs. If the difference is very slight, a thin piece of cardboard will do the trick (see Tips).
Remove any dirt or buildup from the shorter table leg with a rag or stiff brush.
Place the cork underneath the short leg to make sure it removes the wobble. Adjust the cork's length if necessary.
Use wood glue to adhere the cork onto the leg. Wipe away any residual glue with a damp rag.
Allow the glue to dry completely before moving the table.
If an extension leaf of the table is wobbly, insert a small wedge of wood between the tabletop and the extension support (the arm that holds up the leaf).
For a very slight wobble, glue a thin piece of cardboard underneath the short leg instead of a cork. If you are seated at a wobbly table in a restaurant, wedge a book of matches under the short leg to reduce the wobble temporarily.