Seniors are one of the best age groups to photograph.  They are excited about the shoot and thus make for cooperative and enthusiastic subjects.  However, it is best to go prepared for the shoot so that everything goes off smoothly, it turns out to be a fun experience for you and the subject, and you end up with some great portraits.  Here are some tips to keep in mind when planning a senior portrait photograph shoot.

Get to know the senior subject

It is a good idea to get to know your subject before the shoot.  This will make them more comfortable and will help you establish a rapport making it easier to work with them.  Seniors are often very clear about what they want.  Get their input as to what they have in mind for the portrait.  Also give them an idea of what you feel would look best.  Try and ensure the portrait captures their personality as best as you can.
    

Background

Choose the background for the senior portrait photograph keeping in mind the nature of the subject, the light you will be shooting in (day or night), and the look you want for the portrait.
    

Outfit, accessories, and makeup

Choose the outfit and accessories in advance to the shoot.  If your subject has already decided on something, get them to show it to you.  If you feel any changes need to be made, gently suggest what you feel could go wrong with the outfit of their choice and then suggest what you feel would look better and why.  Make sure the clothes are comfortable, the colors stand out against the background, and the outfit reflects the personality of the subject.  For girls, use makeup that complements the clothes and highlights their best features in the portrait.
    

Props

Again, depending on the look you want for the portrait, decide whether you want a prop or not.  If you do use a prop, confirm that the subject is comfortable with the prop you have in mind.  For shy or nervous seniors, a prop helps further by giving them something to hold in their hands, or to sit on or lean on.  Props could range from a hat or bunch of flowers held in the hands, to a bench in a field of flowers, to a stallion in the background.
    

Posing

Once you have selected all the above, decide on what kind of pose you would like for the senior portrait photograph.  Seniors generally enjoy posing and make for great models.  Once they are comfortable, let them pose naturally and keep clicking.  Also, get them to move around so that you get a range of poses.