Standard portraits like the ones that appear in high school yearbooks or traditional family photos may feel awkward to set up, but the positioning of the subject's body and head are important in getting a good photo. Generally the head and the body should face different directions. For example, if the subject is looking directly at the camera then his body should be tilted slightly to the left or right of the lens to avoid a head-on mug shot appearance. You can help add masculinity to a man's pose by tilting the head slightly toward the back shoulder and women can get a more feminine look by tilting the head toward the front shoulder.
If you are shooting a group portrait you should not line everyone up side by side. First of all, you may have a shot so wide that you have to get too far away to squeeze them in if it's a large group. It will also prevent the group from looking unified. Instead, position them either touching one another slightly or overlapping to give the appearance of a cohesive group.
If your subject is wearing loud colors or crazy patterns in her clothing it can make for an unattractive picture. Suggest wearing limited colors and simple designs for the best results. In groups, ask the subjects to wear similar tones of clothing, such as all warm colors or all cool colors. They do not need to wear the same colors, however. If someone has particularly bright colors or is in contrast with the rest of the group, place them in the middle of the group if possible.
Sometimes the best portraits don't look like the standard posed photo. Create a candid feel, as if you were able to position yourself without the subject's knowledge and take the photograph. Of course you won't be sneaking up on anyone, but you can accomplish this look by having her look off camera to create a sense of mystery about the photo and make the subject seem more natural.