See article here
1. Use pre-installed software (use DeCrapifier)
2. Accept Default download and install presets (check for 'checks')
3. Cleaning Registry to 'speed up' PC (you may slow it down)
4. Too much defragmentation of your PC hard drive (Windows does it automatically)
5. Failure to restart your PC (try once a week)
6. Failure to backup PC (use Crashplan)
7. Failure to keep apps and anti-virus up-to-date (check for updates often - install Secunia PSI)