First off, I check what is automatically started when the machine boots up.
- Autoruns
- Registry: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
- msconfig
- Run -> services.msc This will list all the services that are started up when your machine turns on. You can manage all of them here from this MMC snap-in.
- Scheduled Tasks
I will then run process explorer and see what is running after it is booted and see what hogs up a lot of memory and CPU.
I will then make sure all the drivers are up to date, same with anti-virus, windows update and other critical applications such as web browsers, java, flash, etc.
Then I will defrag their hard drive if it needs to be done.
Sometimes I will clear out their web browser history and cookies and also clean out their temp folders.
I will also look through the event viewer to see if there are any errors being reported and check into them if they do.
If all else fails and the system will support it, a RAM upgrade may be in order.