Simple things can make a big difference. Sometimes with wide lenses the slightest tilt of a camera can kill a photo. Sometimes that same slight tilt can make the photo. But to insure a straight camera grab a bubble level for the hot shoe. If you are using a flash or pocketwizard it is simple enough to level the camera and then remove it.
Outdoor Photo Gear sells an awesome bubble level for $20
Thanks for reading and happy shooting,