Exactly what Brit said above.
Yup.
DFK I've always considered to be on the ymmv spectrum. In some ways deep kissing can be the
*most* intimate activity of all.
So it really requires at a bear minimum flawless hygiene:
brushed teeth, flossed, mouthwash, mints or listerine dissolvable strips or mint gum *right before meeting* (literally as you are going up to the house, room, up stairs, elevator, whatever). That's just a minimum. You want to smell good in general, be super clean, fresh smelling hair, nice body smell, well groomed.... Those are all the parts you
can fully control.
The one you
cannot control is the chemistry or attraction level. It's diff for everyone. A handsome guy (in the sense no one would ever call them 'ugly' even if it's not
their favorite) who did all the above prep can probably nearly always get dfk if the girl is even remotely open to the idea.
Now that doesn't mean she is very attracted to him. I mean you could be Ryan Reynolds or pick 'some hot guy' and some women just don't like that (similar to how Eva Mendes is nowhere remotely as pretty to me as Eva Longoria - not even close). She's good looking. For sure. But it's not *my* personal thing. Same deal with, say, Kristen Stewart vs Elle Fanning or Anna Kendrick vs Alice Eve. In the latter of both those I'd kill to be with them, the others are decent, sure, and to some they are better than the latter that I prefer, but that's my point.
If you have those kind of looks where virtually
"no one" would realistically think your
"unattractive" then kissing is a pretty easy activity. If you happen to be super attractive to
them, great chemistry, then a killer girlfriend style make-out is super easy (even with a woman who doesn't usually kiss clients).
The point is twofold:
1) it's largely hygiene (controllable on your part) and
2) chemistry/looks (not very controllable -- yet one 'can' always make themselves more presentable no matter their genetics).