1. Watch heads. People tend to do one of two things when you are shooting straight on, they either bring their heads up, exposing a lot of neck, or they bring them down too much giving themselves a double chin. Try to level their heads to look at you straight on.
2. Suggest to your subject that they wear dark clothing. It is true, black is slimming. This is an especially good suggestion to make to brand new moms when you are shooting newborn photos. Their black shirt makes a great back drop to have them hold the baby against and it will make them look and feel thinner.
3. Shoot from above. Get above your subjects and shoot looking down at them. This is one of the things you have the most control over and is very effective.
4. Twist. Having your subject twist sideways instead of facing the camera straight on will make them look thinner every time.
Using just a couple of these tips, you can make your subjects look their best and give them photographs you'll both love!