1. First of all, people who get offended by lewd jokes probably shouldn't consider working nude. I know that most people tend to be on their best behavior when there is a naked actor on set... but that often doesn't last more than an hour or so.
Now, I'm not saying that after an hour the entire crew will switch into some lecherous mode and start groping the actors. But what I am saying is that I have never, ever been on a horror/action film set where the dirty jokes didn't flow like water regardless of what the scene is. It's called "lightening the mood", and it is actually a very healthy thing to have when you're working with some pretty grim material. So if a weapon gag piece looks like a big phallus, you're probably going to hear some dick jokes. If the boom mic has to be positioned near an actress's naughty bits, you'll certainly hear comments about that too. And as an FX artist, there are some photos of me working on nude actresses floating around that makes my job look like a frat boy's wet dream...and don't think that wasn't brought to my attention when the photos were taken!
2. Closed sets are usually (but not always) the norm when it comes to filming scenes involving nude actors. Sadly, I've been on a couple "closed" sets where the term was used very loosely and made the nude actors on set extremely uncomfortable.
A "closed set" means that only the essential talent and crewpeople needed to shoot the scene are on the set. The nude talent may request a particular person to be there for his/her comfort, or in most cases a trustworthy crew member of the same sex as the talent is on set. (This is often why I'm requested to do the FX for nude scenes, being a female who is also essential crew.)
Now, there may be some argument as to who is "essential" and who isn't, but let me tell you that it is not uncommon at all for a closed set crew to be composed of just the director, the DP with a camera, a sound mixer (if dialog is involved), and a designated same-sex PA. I was on a set once where a very aggressive male script supervisor was making it a point to be as close to the nude talent as possible (including while the actress was in the makeup area) and who literally barged into the closed set yammering about how he was "essential crew". I personally wouldn't have blamed the actress if she had refused to disrobe until he was escorted off the location, and I applauded another crew member who slammed the door in his face at one point. If the talent is uncomfortable with any crew member on a closed set, you aren't going to get a good performance if you allow that crew member to stay.
Also, cameras outside of those being used to actually film the scene are not a good idea on a closed set. Aside from shots taken for continuity purposes or those where special permission is given by the production or talent (as in the case of portfolio material), people snapping photos of nude actors with personal cameras tends to make the talent very uncomfortable. As one actress said: "I don't want to see my boobs all over the internet tomorrow."
3. Don't take a role that requires nudity if you're not 100% sure about it. Being nude in front of a professional crew is not a big deal. Believe it or not, I am speaking from firsthand experience here... I have been known to strip off my blood-soaked clothes right on a set rather than risk creating a blood drop trail to a proper changing room, and no one has ever gawked/drooled at me or attacked me in some lustful frenzy. However, I've talked to plenty of actresses that fear that they'll be ravished if they so much as flash their breasts for the camera.
The professional actresses I've worked with have the same mentality that I do when it comes to stripping off their clothes on a set. They know it's part of the job and people are there to make a movie. They have confidence that the producer did not crew the project with sex-starved maniacs and that if one such individual did slip through the cracks that he/she would be swiftly expelled from the set.
The not-so-professional actresses I've met, well... I can't help but feel that maybe they had to be "talked into" doing the nude scene to begin with, which is always a big risk. Mind you, everyone has a first time doing it, but first-timers chickening out at the last minute isn't uncommon. So my advice to directors is that if the role absolutely must have nudity, make sure that the audition involves nudity (and even then you don't have a 100% guarantee that someone who auditioned nude won't get cold feet on the actual shooting day.)
Another big excuse I've heard from actors is that they themselves don't have a problem with nudity but their spouses or significant others do. To be blunt, I find this excuse to mean that the actor has a partner who harbors jealousy and is not supportive about his/her career. I can certainly understand someone not wanting their partners to do pornographic films, but I'm hard-pressed to think of many popular actors who haven't done at least one partial-nudity scene during the course of their careers. (Great example: Damned near everyone who has ever appeared on Spartacus.)
So whatever the excuse, don't take a nude role if you don't think you can really do it. Many directors have started filming their nude scenes first in order to be able to replace a should-be-nude actor early in production if he/she chickens out. As much as some of us hate to have to admit it... sex sells in this biz.
4. Treat nude actors with respect, but don't pamper them. Okay, I know that sounds awkward. What I'm saying is that you should treat nude actors with a high amount of respect and make sure that they are reasonably comfortable, but you don't need to cave in to every little diva-demand they might insist upon.
I have been on projects where the actor who has the nude scenes thought he/she could just run the show because they were so terribly important to the production. The truth is, finding someone who will get naked for a project is not nearly as rare of a gem as one might think. Go to any adult entertainment club and you will find dozens of people who strip in front of strangers on a regular basis. Porn actors are a dime a dozen and many of them would like a chance to be in a "real" film. And contrary to popular belief, most of these folks don't regularly make a lot of money.
Granted, if you have a known star on your cast who needs to disrobe, you probably will have to meet some demands. But for small productions without name talent this is often unnecessary. Actors with nudity-involved roles should expect the same common courtesy as those who keep their clothing on, and their reasonable wishes should be accommodated when it comes to closed sets, but they should not expect to be put on a pedestal simply because they chose to audition for a role that required nudity.
Read that last part again. They CHOSE to audition for a role that required nudity. Their actor contract should clearly outline what kind of perks they can expect, if any. I have seen actors essentially blackmail directors into giving them all kinds of special treatment on the threat of not doing the nude scenes otherwise. These types of actors should be fired the minute such a threat is made.