Make your feelings clear. 

Breaking up with someone is never easy, but you have to be direct about how you feel. Do not beat around the bush and be as clear as possible about what you want to say to your partner. Being passive or unclear can make this kind of news even worse. It may be easier to be indirect and you may think this is saving their feelings, but all this will do is bring about the opportunity for more confusion and pain. 

Be completely honest about everything. 

There is nothing worse than not giving someone closure. Some people end relationships by just saying that they are done with things. This gives no context or understanding for your partner to make peace with your decision. Being upfront and transparent about your feelings will ensure that your partner understands why things took the turn that they did. This is the best way to give your partner a better chance at getting over you in the long run.