Decide if you truly want to end the friendship
First of all, think about the friendship and decide if you are sure that you do not want to continue with it. This is because when you inform your friend that you are not interested in being friends any longer, chances are he or she will not be pleased and will be ready to take you back if you change your mind later on.
Once you are sure, try to be honest and explain your reasons clearly to your friend. Do not just try avoiding them so that they get the point. If you feel you cannot do this face to face, then call them. You should have the decency to do this over the phone. Breaking up with friends over text messages or email is very inappropriate.
Provide them with a reason
You need to present a reason to your friend for the break up so that he/she can get closure. It will help them carry on with their lives. Tell them if the friendship just faded over time or if you got irritated by his/her presence. Make sure you do not involve other mutual friends in this matter. Also, be mature in your actions; do not talk badly about your friend. Remember it is not wise to ask common friends to side with you. End the friendship on a good note, with no hard or bitter feelings on either side.
Stick to your decision
It is vital to set specific boundaries and stick to them. Do not answer his/her calls or emails if you told them not to contact you while ending the association. You need to be consistent to speed up the break up phase. However, keep the door open for a reunion if you feel the problems can go away later on, and tell this to your friend as well.