I use these tools:
1) Run Malwarebytes (fast) and maybe Spybot search and destroy to clean spyware.
2) Update Windows and antivirus.
3) Run CCleaner + CCleaner enchancer to clean old files from many programs.
4) Run registry defragger like Regseeker of any registry defrag software.
5) Run Auslogic disk defrag to defrag the disk.
Also check memory, free space, unused software, RAM, Extended Memory and I twaek a bit the OS (put Windows RAM use in best performance with just 2 options ..user doesn´t detect anything).
With these tips he/she will notice a GREAT improvement. Plus tell them to use Chrome, sometimes Slow computer is just a slow browser.
Smyth
www.smythsys.es