The best thing you can do is use the Tor Browser Bundle, which is designed specifically to make your web traffic completely indistinguishable from that of any other user of the Tor Browser Bundle.
In general, any active thing you do (changing the user-agent string for example) is much more likely to make you more distinguishable rather than less.
See how unique your browser configuration is here: https://panopticlick.eff.org/
