To make a good confession, we should…

1) …examine our consciences regularly and thoroughly;
2) …wait our turn in line patiently;
3) …come at the time confessions are scheduled, not a few minutes before they are to end;
4) …speak distinctly but never so loudly that we might be overheard;
5) …state our sins clearly and briefly without rambling;
6) …confess all mortal sins in number and kind;
7) …listen carefully to the advice the priest gives;
8) …confess our own sins and not someone else’s;
9) …carefully listen to and remember the penance and be sure to understand it;
10) …use a regular formula for confession so that it is familiar and comfortable;
11) …never be afraid to say something “embarrassing”… just say it;
12) …never worry that the priest thinks we are jerks…. he is usually impressed by our courage;
13) …never fear that the priest will not keep our confession secret… he is bound by the Seal;
14) …never confess “tendencies” or “struggles”… just sins;
15) …never leave the confessional before the priest has finished giving absolution;
16) …memorize an Act of Contrition;
17) …answer the priest’s questions briefly if he asks for a clarification;
18) …ask questions if we can’t understand what he means when he tells us something;
19) …keep in mind that sometimes priests can have bad days just like we do;
20) …remember that priests must go to confession too … they know what we are going through.

From: Fr. Z’s 20 Tips For Making A Good Confession

While we’re at it, here are the words you should say at the beginning of your confession, and then at the end of your confession:

“Bless me, Father, for I have sinned. It is (X days, weeks, months, years) since my last Confession. I accuse myself of the following sins.”

Then list your sins by kind and number. If you can’t remember how many times, say, “I stole candy bars so many times that I can’t remember.”

After confessing all your sins, next say:

“For these and all the sins of my past life, I ask pardon of God, penance, and absolution from you, Father.”