a simple walk creates an authentic look of motion in a photo because you actually ARE moving. a "fake" 2-step walk does the trick as well.
keeping the movement going by shifting your weight, touching your hands together or playing with accessories gives variety to your shots.
while moving, naturally pause here & there by stopping mid-step or leaning or sitting on something for a quick snap.
if you find that your smile in pics comes off too "put on" or fake, try laughing so your photographer gets a genuine smile!
being in front of the camera takes some getting used to, but don't take yourself too seriously. relax & have fun & your photo results will be great!