Prepare in advance what you will say father. This is best done in solitude. Take a clean sheet of paper, pencil or pen and remember all the bad things you've done lately. The first thing to remember mortal sins, they must be written in the beginning. This sheet you can take to confession and read it, so that shall describe everything as detailed as possible and clearly. This will help you in case if you will not be able to speak for themselves. Just ask the priest to read everything that is written on the sheet.
Starting to be valedictorian, be absolutely sincere. You must fully confess their sins. Take the sacrament more seriously, because it is designed to cleanse you and your soul. You need to not just list all your sins, but to confess them, to prove that you really regret it and want to change. And to prove, especially to yourself.
As a rule, the first is a General confession during which the priest can remind about the most common sins, and then individually. Listen carefully to what you say because you may not even be aware that we have sinned. Remember that you can't take the priest too much time, because in the Church a lot of parishioners, and everyone needs to speak. This is one of the most important rules concerning how to confess.
If you are ready for a serious repentance, ask the priest to give you the General hours-long confessions, in which I recall all the sins you have committed since the age of seven. Don't think of what to say to the priest, just open your heart and tell him about all the experiences that have been accumulating in you for the entire life.