How to come out.

I am at the point in my life that I am ready to begin my journey to telling my mother that I am gay.  I am not going to spring the TG issues on her yet, I just want to be open with her about my sexuality.  It has been 7 years since I have been with a woman and I know she is fully aware of that, but she doesn't know a thing about me being with men.  I am not going to dive into the personal stuff at all.  If she asks, I will tell her what I think she needs to know and that is it. 

Why I am writing here is.... How should I approach my mom? How have others done it?  What were some of the reactions?  What should I look for or expect?  I feel like an idiot. I am a grown person and mom/dad (single parent for the last 16 years) to a wonderful honor roll college student and I can't seem to find the 'right way' to approach my own mother.