If you know you're gonna have to do it, don't wait
Don't do it over text
Don't be mean about it or hurt the other persons feeling purposely, this is probably already hard enough for them
If the relationship is toxic or dangerous end it immediately and cut off all ties with the person
If they try to convince you to stay with them, don't. You made your decision and you made it for a reason
Make sure you tell the person why you're making you're decision
If you've lost feelings don't lie and say you still have them and don't force yourself to try to feel it again
Don't be afraid to stay friends if the relationship was healthy while it lasted
If the person is giving difficulty about breaking up bring in a trusted adult
Don't involve friends in the break up it will cause a lot more drama
If the person is still attached to you in unhealthy ways, talk to a trusted adult or professional, they may be able to help the person
Hope these helped! Good luck!