If you're in major market, contact one of the MFG or major distributor.
Most will be happy to take an hour or 2 to sit down and discuss good design practices.
Other than that, experience will teach you.
Walk into WalMart and look. Actually, before you ever get inside, check out the number of cameras they have on poles, walls and every corner. Drive to the back.

Hollywood (CSI, NCIS, etc.) has taught us that 1 ATM camera can somehow see around the corners and image can be 'enhanced' to see person's fingerprint from 300 yards away.

Don't put cameras pointing straight down or all you'll be able to tell is person's bold spot.
You'll need 2x or 3x as many cameras as you think.
Don't just install one 2.8mm camera and think that just because it has nearly 90deg FOV that you'll be able to make out who's at the door 30 feet away.

There is more, so much more...