1. Run a disk cleanup and defragment the hard drive.
2. Uninstall unnecessary programs.
3. Disable startup programs that are not needed using task manager or msconfig.
4. Update outdated drivers, especially video drivers.
5. Scan for malware and viruses.
6. Increase RAM if possible.
7. Look into overclocking your processor if you have an unlocked one.
8. Enable Windows sleep mode or set the computer to hibernate after a certain period of inactivity.