So, I'll talk about things other than genitalia, since that seems to have been covered extensively here already (and I honestly don't do many full nudes anyway).

Things that are important in getting realistic renders:

1. Facial structure and expression:  Unless you are very far away, the face makes or breaks the image.  Everything else can be absolutely perfect but if the face is wrong, the image sucks - end of story.  Looking around the galleries I'm always amazed at the  many downright bizarre looking faces that people put into renders.  I'm not talking ugly, I'm talking malformed - eyes slanted to extreme angles, eyes bigger than your fist, lips contorted into nearly triangular configurations, lips extending inches out from the face plane, noses that are impossibly small and flat - so many problems.  I always create the facial structure myself using various morph kits I've obtained.  My best faces almost always come from working off of a photo reference or two.  Anyway, however you get your facial structure, make very sure that the face you end up with is possible for a human being to actually have (Michael Jackson excepted).   The same goes for expressions.  First of all, make sure your model has one.  Then make sure it's not breaking her face.  The millenium women have real problems going through a wide range of expressions without the geometry looking bizarre.  Jessi and Miki are much better at this.  Also make sure the eyes aren't just staring off into space - it doesn't take much, just tweak the up/down, right/left parameters on the eyballs.

2. Texture: A good texture can cover a multitude of other sins.  For women, my all time favorite texture is Sirya which you can pick up here: http://www.zs3d.com/   I've been meaning to pick up Xunah for a while (I've been holding off on buying V3 specific stuff for a while waiting to see what "new" character is introduced), but she looks stunning so I'll probably knuckle under and buy her soon.  Other Textures that I use often with good results are Annabel by A_, Sierra Sage by Morris,  and Ioana by Vali and Nicu - all available here at the market place.

3. Lighting: Honestly I've yet to see one light set that works for every situation, I don't think there is one.  I still suck at lighting, but some times I get it right for an image.  For most work I use just two lights - one infinite and one ibl.  This gives me consistantly o.k. results with minimal effort, but usually I can't achieve anything breathtaking with that.  You'll have to experiment to get the best results for you and the particular scene.

4. Material effects: Just go out an get the FaceOff realism kit for your chosen figure - it's the best purchase you can make after getting an excellent texture.  Pick up the occlusion master as well if your character is going to be wearing anything or be in a pose where it intersects itself - the extra realism in the shadows is well worth it.  Here's a thread of mine that I devoted solely to getting good eye effects in Poser 6, my settings are in there if you choose to use them - http://market.renderosity.com/mod/forumpro/showthread.php?message_id=2460673

5. Render settings:  Be sure you've got them set to a high quality to achieve best results (I posted another thread about this last week that I'm still planning on following up on that contains settings I use that give me good results) - http://market.renderosity.com/mod/forumpro/showthread.php?thread_id=2645790

6. Hair: Obviously it depends on the style you want, but if you don't care about style it's hard to go wrong with one of Koz's free hair props/models.  They render quick too, unlike some other hair props/models.

7. Pose: Needs to be realistic, needs to not cause breakage/cutting.  Most kneeling poses don't work because of the collisions between the upper and lower leg - even joint parameters don't fix this one.  You'll need to use magnets or some other morphing agent to make them work.  Most people used canned poses (myself included), so this one is a bit easier to deal with and this comes lower on the list for me.  Schlabber not only makes great pose sets, but also has an excellent posing tutorial on his site.

After that it depends on what the rest of the image composistion is - but really if you don't get the above right the rest of your composition isn't going to mean much (assuming the figure is the main focus of the image).

Hope this helps some,

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