First, try using a plunger. Second, try using a liquid drain opener, but use caution and read the directions. Third, you can remove the trap and remove any debris. Be careful if you have used a liquid drain opener, because there may be some in the trap. Fourth, if the clog is beyond the trap, there are drain augers that extend from about 15 feet to about 50 feet. There are also special active bacteria based drain openers, like Benjamin Franklin Plumbing’s BioBen, that will help dissolve buildup in pipes in older homes.