1. Check the timing.
No point trying to discuss a problem if the other person can't/won't listen. It's kind've a no-brainer.
2. State the facts.
Don't be vague; let the person know exactly what's bothering you in a non-accusatory way. Specifics, people!
3. State your feelings.
You still don't get to lash out, but let them person know that their actions make you sad/upset/scared/whatever.
4. State your needs.
Tell them what you want/expect them to do to fix the problem.
Ask the other person for a response.
Get feedback! Open up dialogue!
Easy midterm! Unfortunately it was scheduled at the beginning of class, so I still had to sit through everybody else taking it and two more hours of class.
I was totally going to ditch early, but when I walked out the door the teacher asked me directly "Are yuo really leaving?" and I felt guilty and just ran out to my car to get my cell phone instead.