Use Ccleaner monthly (wekly is normaly overkill) to cleanup left over files and clutter and check your registry.
Defragment your drive regularly. Once a year is NOT enough, do it at least every 3 months (ABSOLUTE minimal interval for a conventional drive). Use an alternative defragmenter as the bundled one is not effecient. Defraggler is an excellent free one and have sheduling. It allow you to set it and forget. A wekly shedule is good.
If you have an SSD drive, you must NEVER EVER defragment it as it have an adverse effect on it's life time.
Some good, and free anti-virus: AVG, Avira, Avast.
Set to automatic wekly scan, daily virus definition updates and at least monthly engine update checks. Set it to automaticaly scan any downloaded files (should be enabled by default).
Some good anti-crapware: Spybot, Ad-aware.
Run manualy every 1 to 3 months.
To open the task manager, hold Crtl+Shift+Esc.
You can quickly switch user by using the WinLogo Key + L.
Check your startup list. Remove anything you don't realy need or want.
Check your notification area. If you have any quick starter, disable them. This usualy mean unchecking something like "Load with Windows" or "Start with Windows". Those are useless and slow you down.
Chrome is a good browser, another option is Firefox.
On both, install AdBlock.
Whenever you install ANYTHING, always take the time to actualy read the dialogs. Always decline any side or accessory offers, especialy those mentioning any tool bar, search engine or home page change. They are never needed.
It often mean using the "personalised" install instead ot the default one.