Purchase four 2-inch-by-2-inch lumber beams from a lumber retailer or home improvement store.
Measure the height of the table with a tape measure, then measure and mark the 2-by-2 lumber beams to cut to that height.
Put on safety glasses and a dust mask. Cut the 2-by-2 lumber to fit the table height with a circular saw.
Sand each leg to remove any splinters and to smooth the wood surface.
Turn the tabletop upside down, laying it on the floor. Squeeze glue onto the top of each leg, then place each legs into the four corners, fitting tightly against the table top skirt.
While the glue is drying, fasten L-brackets to the legs and skirt with a screw gun. Fasten two brackets to each leg. This, along with the positioning against the skirt and glue, will make the table legs very sturdy.
Turn the table upright after the glue has sufficiently dried. Consult the glue label for suggested drying time.