Recommended Weekly Cleanup Procedure

1- Update Virus Definitions. Note that this does not mean update software, but update the virus definitions. eg for some programs call these DAT files.

2- Update Anti Spyware definitions, again not the software but the spyware info.

3- Run system updates, to get security items, ignore other items for now(use custom always, since MS pushes updates for their office and live products). Note driver updates are not necessary unless issues are occurring , this should be last resort, especially if original disk to drivers is not to be found.
for Windows:
IE->tools->update
or Run->cmd, then type wuaucld.exe
or Run->cmd, services.msc , then for 'automatic updates' right click then select start

4- Clean Hard Drive
a) Clean Temp directories, in Windows use Disk cleanup, select 'my computer' then right click on 'C' drive in windows explorer, select 'properties' button, then on 'general' tab, under pie chart select 'disk cleanup'
b) For Internet files and cookies, do this by means of the web browser.

5- Clean Registry - must have admin rights
a) Backup First !!!!!!!
Run->cmd, then type 'regedit', then select File->Export, save this to c: drive and name it with date and time, so it's easy to find
b) use tool such as ccleaner or sbmav cleaner
c) if the changes are issues after reboot, just start in safe mode and start regedit(step a) and do file->import, and use the reg file from step b)

6- Run Full Virus scan, if takes long, then run in the evening when no one is using PC and won't be interrupted

7- Run Anti-spyware cleaner

Monthly
Review disk space usage, by using programs as:
tree size
tweak now-> disk usage analyzer
space sniffer
These will reveal directories that are taking up space or programs that are space hogs. However, use your discretion when deleting files in directories manually(delete button). If not sure....better to leave alone and get advice on a PC forum. Always use the uninstall programs with apps, since these will remove lingering registries settings.