When drying your clothes normally you check your lint trap after every few loads. If the lint has built up you remove it, insert the filter back into the dryer, and dry the next load. One thing I learned a while back is even though you think removing the lint frees up the lint screen after time there is hidden build up on there that can damage your dryer or even create a fire.
If you've never done this take your lint screen out and take it to the bathtub. Run some water on it. Does the water fall thru or is there a layer of film on the screen that doesn't allow the water to fall thru. If so imagine what is happening when drying your clothes. If the water doesn't pass thru easily it's time to wash your lint screen.
At least every six months you should pull out your dryer screen and wash it with water and a scrub brush to remove that filmy layer. Not only does it help in drying your clothes but will also cut down on costly repairs on your dryer and possibly a fire.