Your kitchen faucet gets heavy use on a daily basis. Swiveling the head from side to side and other normal actions can loosen the faucet if it is not properly fastened, causing the unit to be unsteady and shift around on the edge of the sink. Tightening kitchen faucets often takes two people simply because it is difficult to reach the fasteners while holding the faucet steady at the same time. To keep your sink tight once it is fastened, you may be able to add an adhesive to the fasteners' threads or install a locking washer above the nut to keep it tight.
Remove any items from under your kitchen sink to allow yourself complete access to the plumbing.
Position your upper body beneath the sink so you can look up behind the sink bowls to where the faucet attaches.
Shine a flashlight at the faucet connections and determine how the faucet is attached to the sink. There may be one bolt beneath the faucet spout itself, two bolts on either side of the spout, or nuts that tighten around the entry holes for the water lines and spray hose. The bolts may be traditional, threaded metal or short, relatively flat plastic, or a combination of both.
Ask a helper to position the faucet and hold it in place from above the sink.
Turn any nuts or connectors clockwise to tighten them. Hand-tighten plastic or wing-nut connections, or use a adjustable crescent wrench to tighten metal nuts. Special wrenches that fit into tight spaces are often available at hardware stores.
Ask your helper to wiggle the faucet. If he is able to do so, tighten the nuts further or look for a nut you may have missed. Repeat until your faucet is secure.