Slide the drawer out and remove it. If it has wooden runners, spread paraffin wax liberally along these and along the tracks in the dresser. Sometimes the edges of the drawer act as the runners; if so, spread wax on these. Replace the drawer and slide it back and forth a few times to verify that it works better.
Spray lubricant on the tracks and runners of drawers if these are metal. If the drawer has wheels on the side that move along tracks, spray the wheels and make sure that they turn freely.
Remove the drawer and inspect the alignment of the tracks and runners if lubrication does not solve the problem. Check to see if screws or nails have come loose; if so, tighten or reattach them.
Use a hand plane or a belt sander to remove wood from the runners if the drawers have swelled and are sticking because the are too wide for the opening. You may have to remove a little from the edges of the drawer front as well.
Reglue the drawers if they are coming apart and this is the reason they are sticking. Separate the loose joints, spread carpenter's glue on both sides of the joint, then clamp the drawer with a bar clamp and let the glue dry.