Standing
Whenever you are taking a picture of someone standing, you never want them standing square to the camera. You should always have the person turned at a 45 degree angle and have their head turned directly towards the camera. This minimizes the width of the person and creates nice line from the shoulders being turned.
Sitting on Floor
There are many different poses you can use in this position. Some of the most common are having one leg bent at the knee close to the subject's chest, with their arms rested on top of the knee. This creates a very casual pose, and adds depth with the arms being slightly in front and below the persons face. Another version of this pose is for the photographer to shoot it from the side, have the person slightly extent the raised leg so it is not as high. The person then rests their head in their left hand has their elbow rests on the raised knee. The other leg can be folded close to the person or extended straight out.
Three Quarter Pose
This picture is very similar to a head shot type of image, but is expanded to include the person's torso. You follow the same method used in the full body standing pose where you place the person at a 45 degree angle towards the camera. The difference is what you can do with the person's arms. Depending on the type of portrait you want to create, you can have them standing with their arms crossed for a strong pose. Have the person bring one arm up close to their neck or shoulders for a softer more vulnerable appearance. You can also change the elevation of the person's shoulders raising the one that is the furthest from the front of the camera lens. Doing this adds another element of angle, this creates a different line in the picture.
Using Props
Adding chairs, benches, beds or other props into a portrait changes the picture entirely. You can have the person lean on the back of the chair, or sit on the top of the back of the chair with their feet on the seat of the chair. Use the props to further enhance the type of picture you want to take and don't be afraid to try different unconventional poses.