[header] How to tell someone you're an atheist [title] Know what you want to say. [step] Having your talking points planned out can be a huge help. This will allow you to focus on the important parts of the conversation and get your message across to the other person. 
If you need to, practice in front of a mirror or write out your main points before the conversation. [substeps] An example of something you might say would be " i know that the rest of the family is religious, but i simply do not believe the same things.