So, I was wondering how you guys initiated a changed from one position to the other. I've always just asked, but maybe I'm doing it wrong.

The way I usually do it is just start to kiss and begin to sit up, drop your free hand somewhere below the waist, twist and rotate on top...or start to kiss, place both hands on the chest, wrap the leg that's free around his/her free leg and rotate...a little agression is good sometimes.

Not sure I understand the question, it is best to express your desires, I guess you could just flip her ass over but she might not care for that. LOL

Just like you'd signal before changing lanes, otherwise someone could get hurt.

lol,been there done that.
I prefer you to say what you want when you want it at all times. It turns me on.
mish.doggie,cowgirl,ect.

You can also ask her to initiate the change - keep you interested, and her purring warmly....

If I am having sex with a provider missionary, and I feel like taking her doggie, I'll just stop and say, "I'd love to take you doggie, now" I have never had a provider say no. It's a very simple system!

roll over
lemme get on top
put your foot over there

adding bitch and smacking her ass might help.

might not