Hi , if it is a normal manicure with polish I would do that first as the nails will dry thoroughly whilst the client receives the facial.
If gels then it really is up to you, but again i would probably do nails first .
If it's a manicure with normal polish then do the nails first but before you paint get them to remove top clothing & straps. Offer them a towel or something to go over their shoulders to keep them warm.
Once they have wet nails then guide them over to the couch for their facial. Ask them to lie down and then raise their arms. Then you put your top towels and blankets over them and tuck them up without anything touching their hands. Place a small towel over their tummy and tell them to place their hands down carefully on the towel.
If the room is cool, place another towel across their shoulders to keep them warm but hands still sticking out.
If they want gel polish then it's no problem. I would still do the manicure first though. Get the chit chat out the way, then they can nod off in the facial.
I usually see how I’m doing for time, I’ve done manicures while face masks are on and then done polish after, which is super relaxing for the client; or you can prep first and polish while mask is on. Benefit to that is they are still and less likely to smudge if they just lie there than if they were on way out and paying.