There are two causes of a wobbly table: uneven legs and an uneven floor. Legs can become uneven from wear, from warpage (on any of the table parts) or from simply not standing straight. Floors can be uneven because, well, because floors are almost never perfectly flat. But none of that's really important. What matters is that you have an uneven table and you don't want to fix it by cutting down the legs. No problem.
Tighten It Up
First, make sure the legs and all of the hardware and glued joints on the table are tight. This alone might solve the problem of uneven table legs. But even if it doesn't, you want to make sure everything's tight because doing so might change the positions and relative heights of the legs, and there's no sense in curing unevenness on a rickety table. Once all the joints are snug, reposition the table to assess the problem carefully. This will help you determine the best course of action. We'll start with the easiest solution first.
Rotate the Table
This might seem obvious, but often simply turning the table to find the sweet spot where all four legs make contact takes care of the wobble. Round tables are infinitely adjustable, while square and rectangular tables can only be moved at 90 and 180 degrees, respectively, without changing their orientation.
Slipping some kind of shim under one of the legs is another classic solution to uneven table legs, but there are several techniques that work better than the makeshift shim of a folded napkin or matchbook used with restaurant tables. The most basic version is a clear plastic wedge designed just for this purpose. These are small (and clear) so they're not noticeable, and they have little ridges to help them stay in place. Homemade versions of the wedge include cedar shims, which you can score and snap to size, and pieces of cardboard. For a more permanent and discreet shim, cut a disc from a wine cork at the desired thickness, using a large kitchen knife or fine wood saw. Hot-glue the disc to the "short" table leg. You can also apply the same principal to self-adhesive felt, plastic or rubber furniture bumpers. And you can fine-tune cork or plastic shims with sandpaper, if necessary. Shimming is the best approach with metal legs, since the following solution usually is not an option.
If the table's stance is too far off for a shim and you need a sturdy, permanent fix, you can extend the "short" leg with a short lag bolt or even a stout screw: Drill a pilot hole directly into the center of the leg and parallel to its length. Since the leg is probably hardwood, the hole diameter should be at least as large as the bolt's shank (not the threads) or even slightly larger. Drive in the bolt carefully, making sure it won't crack the leg, but don't drive it all the way. Set the table in position, and turn the screw in or out as needed for a perfect fit, just like a height-adjustable leg on an appliance. You can also add a felt bumper under the bolt head to prevent scratches on the floor.
Philip Schmidt is a Hometalk - http://www.hometalk.com - writer. Read more articles like this one - http://www.networx.com/article/easy-fixes-for-uneven-table-legs - or get help with your home projects on Hometalk.com.