20 fps,
well there is alot really. Remember you can open the console in the tremulous main menu.
Firstly connect to a low ping server to start.
Next adjust your com_hunkMegs, com_soundMegs, com_zoneMegs so that you are using a reasonable amount of ram to work with.
Furthermore adjust your com_maxfps, if its already pretty high then you may want to scale it back to like 60 or so, that way you aren't wasting processing time when it does get up there.
Next if texture compression isn't already on turn it on in the options menu.
Not sure if trem has it but you can try setting your r_maxpolys and r_maxpolyverts to something a little lower but becareful.
You should also take a look
here to see if there is anything else you think you can change. Especially look under the tweaking part.
