Closing unnecessary programs can help a little.
Disabling antivirus should just be done all the time if you're capable of
browsing the web responsibly. Holy hell what a memory chugger, even when
disabled.
Visual options in games is a good way, just make sure you're reducing the
correct ones. Some options will actually slow the game down more.
Overclocking your CPU is dangerous, and I definitely wouldn't recommend it.
Same goes to the firewall as it does to antivirus. You shouldn't come across
problems if you don't do stupid things on the net. Firewalls shouldn't slow
games down though.
I would suggest updating the drivers for your video card, that's usually the
best way to get more speed out of a machine. Otherwise your best bet is to
upgrade or buy a new computer. If you go the upgrade route, target the video
card and RAM.
