When ending a short-term relationship, avoid using cliches(e.g. it’s not you, it’s me)if you are hoping to stay as friends. This will break any chance of that from happening. I know from personally experience.
Be honest about why you wish to break up with them, and this will ultimately help them move on. In addition try to be clear about your intentions with them after the break up, and make sure they will know that you will only be friends or less depending on your situation.
Finally, if you are living with the person, try to tell them inside your home (unless it is an abusive relationship, do not do this) that way you aren’t embarrassing them and shows that you respect them. Remember this is only for ending a short-term relationship, some of this may work for long-term but it is not advised since their are many variables between short and long-term relationships.