I like to take out and clean the trap under the sink from time to time. Its seems to help me. But yeah, stick a bucket under the pipe shaped like a "U". Unscrew it, take it out and clean it. Screw it back in. There are also small plastic thingies that often come with chemical uncloggers. They are usually a foot or two long and have jagged teeth on them, ram that down your drain a few times and pull it out. You'll probably pull out some hair, soap and crap like that.
sprinkling baking soda and then some vinegar down the drain and allowing that to do its magic. i've also found that a plunger helps, but the trick is to plug and fill up all sinks and bath tub drains with at least an inch full of water before you even begin to plunger that drain. it helps somehow.