After one too many spilled drinks, you may decide to do something about the wobbly table you're using -- and in most cases, you'll wish you had done it sooner. The fix is usually easy; in fact, you may be surprised at just how easy. Barring some defect in the table itself, it's a mathematical fact that rotating it around its center of gravity compensates for an uneven floor -- you're guaranteed to find an orientation that is wobble-free. When rotating the table isn't an option, you can always place shims under the legs.
Remove everything from the table and turn it over so you have access to the bolts holding the legs to the table frame. Tighten these with a wrench. If the legs are attached with screws, tighten the screws with a screwdriver. You may notice a crack in one of the legs, part of the frame or the underside of the table. If so, it's time to get the table repaired.
Turn the table upright and place it where you want it. If it still wobbles, that probably means the floor is uneven, and there's a simple remedy for that. Keep the center of the table in the same position with respect to the floor and rotate the table. At some point -- often after a quarter turn or less -- you'll find a stable position. This technique works especially well with round tables.
Look for gaps under the legs of a table you can't rotate. Place rubber wedges in any gaps to shim the legs. Don't' use cardboard, which compresses, or wood, which can slide out. Rubber wedges are available at hardware stores, and you can cut them to the size you need with a utility knife.