The stuff in post 8 referenced above is great (on phone, can't quote). My tips below:
Smart defrag 3. Great freeware app (although they try to install a dozen bloatware programs when you're installing to make money, so pay attention). It will defragment your drive better than Windows, plus has a set it and forget it auto option. Start here if your pc is slow when opening big programs.
CCleaner. Reclaim space you didn't know you lost, fix some registry issues, clean up your start up. Clean your start up if your pc takes forever to start when you turn it on.
Avast anti virus. Best freeware antivirus, it's freemium but the paid features are for soccer moms and paranoid old people. It'll clean crap you didn't know you caught from all those adult sites
That's my holy trinity.
Oh, plus one: get Secunia. Free program which makes sure all your other programs and drivers stay up to date, it will also help you download and install updates. It's the cherry on top.
If your pc has a few years on it, adding more RAM can also help speed it up and squeeze a bit more time out of it. Look up your computer properties for your current RAM, and Google your max RAM online. It might cost you like $40 at best buy and take 15 minutes with a screwdriver, but is worth it.