ALWAYS please state your OS - Operating System when posting these types of questions as it helps us troubleshoot and give us better answers. If you went to a car mechanic and asked for help, don't you think he/she would ask what kind of car you have? The same idea applies here.
You could either install more RAM (as much as your MB will support) and/or defragging your HDD on a regular basis will also render some minor improvement.
The other thing is that sometimes there are alot of background services and/or applications that can soak up your system resources and make the entire system run very slow. This is where knowing what OS you're running is helpful.