I love taking portraits.... in fact, that's my favorite area of photography. I'm still learning though.
Doing portrait well by itself is a complex process and it's not something one can give you a "tip" and you can do it. Senior photograph is a specialty in itself as well. You have to know what kind of poses works and doesn't. There are certain things to look for in each of them. On top of it, lighting must be considered. Digital or analog makes no difference. Portrait is portrait.
What is your experience? What kind of help do you need? Poses, lighting, or do you have something in mind and just need help in pulling it off?
That said, the best I can do for you is to give a dump list of what I do. It's too late to "take your time and learn" because it needs to be done now.
To me, finding a suitable location is a big problem. The location must be attractive without distracting objects. Also, it has to be well controlled in terms of lighting. No direct sun and diffused open shadow will make your job a lot easier. Make sure no obvious shadow is falling on your subject's face. Make sure the face is well lit and catch light (sparkle in the eyes) are there. If necessary, use a reflector or two to compensate/adjust/create the necessary lighting. Make sure the focus is accurate and on the eyes closest to the camera. Unless the background is meaningful to the composition, I tend to put it well outside of DOF to bring attention to the subject.
Make sure subject's clothing is right. No attention getting graphics, overly revealing clothing, and watch for wrinkles. If any jewelry is worn, make sure they are in the right place. Take variety of shots, full length, half, and head and shoulder. Typically, nose should be pointed to the camera but body plane face plane should not be parallel. (in other words, face points to the camera, body points elsewhere - body "twisted" somewhat) One foot forward and put a weight on it to create some movement.
Um.... and have fun if you still can....