Three important rules for breaking up:

Don't put off breaking up when you know you want to
Prolonging the situation only makes it worse
Tell him honestly, simply, kindly, but firmly
Don't make a big production
Don't make up an elaborate story
This will help you avoid a big tear-jerking scene
If you want to date other people say so
Be prepared for the boy to feel hurt and rejected
Even if you've gone together for only a short time,
And haven't been too serious
There's still a feeling of rejection when someone says
She preferres the company of others to your exclusive company
But if you're honest, and direct
And avoid making a flowery emotional speech when you break the news
The boy will respect you for your frankness
And honestly he'll apeciate the kind of straightfoward manner in which you told him your decision
Unless he's a real jerk or a crybaby you will remain friends