One of the first lessons I needed to learn was the height placement of the camera. Too high (probably the most common mistake) and it won't trigger (or it will be taking pictures above the animal) because it will be aiming above the deer you are after.
Also aiming down an animal trail will help instead of aiming it so it is perpendicular (even with a fast triggering camera).
I agree with the tips mentioned above regarding the direction the camera faces as well as the trimming of vegetation in front of the camera. I've actually had very good luck with one of the cheaper cameras (the tasco brand) They are not great "trail" cameras, but rather they work well over a bait source or scrape. I have only owned two however, one was destroyed by a bear and the other I've been using for three years and have captured probably over 10,000 pictures with it. My higher quality cameras have better trigger speed and battery life and I do trust them more for an extended stay in the woods.