We always have a quick check in when getting sexual with someone new about what all of our limits are. It means no one has to worry about that "during" and we can all just have fun. And if there are any updates or changes, we talk about those too. It's so simple and so normalized now that I can barely remember not doing that.
Spitting is definitely one of those hard Nos that I haven't even mentioned in the past, because it seems so obviously not something I'd want, but I think I need to add that one in just to be sure.