Just be prepared for a bad result. I thought my sister would be the easy one to come out to, but as it turns out she is having the hardest time accepting it. She also still feels pretty hurt that it took until now for me to be able to tell her as we have always been very close. I know she's going to come around, but I was really caught off guard by her reaction. So I would go into it expecting the worst, it's a lot easier to adjust to being pleasantly surprised then it is to adjust to a disappointing reaction.