Basics are;
Remove all unused images, videos & audio. Just do a regular search for *.jpg / *.bmp / *.png / *.wma / *.mp3 - etc... finding all the unused images, video & audio.
Go to your Start - Startup and delete anything in their, (it is just a link, not the program). Then find and use a good tune-up program, I like TuneUp Utilities, but use what you like or have. Those programs will help with everything mentioned in here.
Turn off ALL automatic updates. They just slow down your computer, and take up needed resources.
Turn off screen saver, desktop images. Just use the power shut down for a lap-top.
Go to 'Control Panel' add/remove programs. Go down the list, many times you will have several "Tool Bars" that are really not needed. Plus look through and delete any programs you haven't used in awhile. Most can be gotten back for free if you change your mind later. Just keep any paid programs if you still want it in the future.
Many people use CCcleaner and swear by it, but I use another.
Do a thorough Defraq, and clean-up from your "System Tools".
After the basics, see how much better it is, then you can do some more drastic things, but try these things first.