This is where a basic photography class could be helpful. There are all sorts of considerations for lenses, angles of view etc. Here is a simple rule to help you out: if you are shooting miniatures—imagine there is a tiny crew of people shooting your film.
Where would they put their little camera? If you are shooting an interior—put the center of the lens about where it could fit in that room.
Then pick the focal length that shows what you need for the shot.
This is just a starting point. Get books on cinematography. Watch great films. We hope this helps!