I also recommend asking before your pants hit the floor. For me, during the M&G is the best time to have this discussion, especially since some NO's are deal breakers for me.
But I approach it as a "here's what I like" POV, rather than a "will you do this" approach.
Examples:
"I love deep kissing... there's nothing more stimulating than a great make out. I find it very intimate. How about you?..."
"I get tested every month and hope you do as well. It's important to me because I don't do well with condoms...."
"I find my best experiences include lots of mutual oral and I love to finish inside..."
With most of these statements I leave those "3 dots" just hanging in the air and I look at her for a reaction or response.
Note that this works best face to face, once you have established some rapport and good vibes. But it can be done through off-site text or video chat if needed.
So it's really my "yes" list as opposed to her "no" list. You will get a really good idea of her comfort levels with this approach. And she will typically either agree or decline quickly. I've had a few discussions like this where the POT asked for some time to think about it (usually due to the BBFS bit). That's probably not a good sign, as she may eventually decline, or may come back with a much higher ask than you can manage. But sometimes, it's all good.
Life is good
The Cat