When it comes to sex, before you get drunk of the chemistry, how much do you know about the person you are about to lay with?
Firstly you gotta be on point with the visual checks. Does he have a sore on his lip? Does his skin have excema like patchy areas. What is his general hygiene like? Any oddities around the genitalia? Pubes clump free in the bush and sack?
How would he respond to sex with no protection?
Does foreplay involve grinding his raw dick on someone's ass or vice versa?
The key for someone to be open with you sexually is to make them feel at ease with confiding their info in you. Also be firm and direct about your boundaries.
Make sure he gives you the heads up before bussing in your mouth to allow you the choice of how the climax is going to end.
Above all, don't do what you don't want to do. Never get sucker punched into thinking the because the two of you are naked when, you are not feeling like taking it to that level, that you 'might as well'.
You've only got one life. Protect it!