I'm not specialist, using Vue5inf.
In addition to what says Helgard, above,
if it's for previews, i get rather fast results with "personal settings",
lowering number of rays,
turning off reflexion (and/or transparency) if not needed,
turning off all anti-aliasings.
No compression, one, max two lights only, no lens flare, no infinite planes in render. Also, glowing mats take time.
But, if your scene is more FX and lighting, than polygon, disabling all that would leave nearly nothing...
Put unseen objects outside the camera's FOV on "invisible" layers.
Verify, if there ain't a small object with zillions of (notnecessary) polygons in the scene.
I first render some frames on screen, to see if it runs ok, then render to disk.