Are there any general rules about FOV and the aspect ratio of your images?
You can pretty much set these to any values as its art and almost anything goes.
Wide FOV's (greater than 90 degrees) tend to have that "dramatic" and distorted look to them, and low FOV's (less than 40 degrees) tend to have that zoomed in "relative scale" look. So use either for whatever effect you are after.
As for A/R, wider tends to match human perception more, but it could really be anything depending upon what you want.
The fov really determines the "zoom" of the camera lens. Something like 50' is considered normal, a value of 60' is considered wide angle and is often used for landscape photography. Anything above 90' becomes very distorted. Use values lower than 50' for closeups.
Here's a good demo:
http://www.usa.canon.com/app/html/EFLenses101/focal_length.html
As moodflow says pretty much anything goes, it's a matter of artistic judgement.
As a rough guide you can usually get away with a FOV of up to 80 degrees (Long axis) on a 16:9 render without unpleasant distortion at the corners.
Cool, thanks guys. That Cannon demo definitely cleared things up for me about FOV. I though it was something that needed to be matched to A/R to get an image that wasn't stretched or distorted along the width or the height. Which I guess it kinda is, but not to the extent I had imagined.
The virtual camera used in TG uses a different projection method the a real camera lens so the distortions produced are slightly different, features near the corners are stretched rather than curved but as a guide the camera demo is a good guide.