>>1
1. Do not use Internet Explorer. Too many reasons to list, several of which means dozens of megabytes of RAM being wasted.
2. Don't run stupid shit. Anything that sits on your system tray when you're not using it is stupid shit. No, icons there are not cool, and you're not collecting them. They are really stupid shit.
3. Don't use bloatware. For example, use BitComet (native C++) instead of Azureus (Java). Run Windows 2000 as opposed to XP/2003, or at least disable themes (oh but they're so cute!).
3. Set services you don't need to Manual, following this guide:
http://www.blackviper.com
4. Run antispywares and get rid of all the shit.
etc