Breaking up is hard to do, and sometimes it is almost worse to be the one who initiates the split. Although every situation is different, there are some crucial points to take into consideration when breaking the news that you no longer care to be in your relationship -- especially if the other person is caught off guard. Ending things in a mature fashion (if possible) will benefit both of you, so to read more,

• Honesty, honesty, honesty
• Make sure you are as sure as you can be about your choice to end the relationship before initiating "the talk"
• Although you have probably confided in friends or family about your desire to split, be sure you are the one who breaks the news to your partner. You don't want him to hear it through your best friends, boyfriends, cousin, etc.
• Talk to him when you are calm, collected, and most importantly, sober
• Choose a neutral, private place to talk, and do it in person. Avoid your favorite restaurant or coffee shop as you never know the outcome of your conversation and you don't want to associate your favorite place with a break up
• Allow yourself enough time to really talk everything out, but it might be a good idea to have a plan for after you have "the talk". Your partner might want to talk and over analyze every situation, and talking in circles won't do either one of you any good
• Give each other the closure you both need to move on. If he has questions, answer them. Make sure you say everything you planned to say as you don't want to walk away feeling like you left anything out
• Although you are ending the relationship, reassure your partner that you won't forget the good parts of your relationship. Try to focus on the positives rather than the negatives
• If your partner tries to makes deals or promises, chances are if he or she hasn't changed when you were together, he or she won't now either (although every relationship and breakup is different)
• If he or she lashes out at you, throwing low blows or saying hurtful comments, keep in mind that he or she is simply upset and trying to make you feel the same pain they are experiencing

The most important thing to keep in mind is don't postpone the inevitable. Once you realize things aren't working out for you, if you aren't honest with your partner, you are bound to push them away subconsciously leaving them more hurt and confused than if you were to simply speak your mind.

I hope these tips are helpful if you have to do the unfortunate, ending a relationship. Good luck.