Remember What a Smile Feels Like and Not How it Looks
Take a minute and try to imagine what you look like. Chances are the amount of detail you're able to conjure up in your mind's eye is about as detailed and accurate as a self portrait you made in grade school. When you're in a photo, however, you try to look good by replicating a visual memory. You know what a smile looks like, so you make one. The problem is, this doesn't work. You need to remember what a smile feels like and not how it looks.