Basically, customize everything you can for the better, and leave as few things as you can at their default settings. This includes the figures, camera, lighting, textures, etc.. Poser does not produce stunning renders right out of the box, you need to set it up manually just as you would a real photo studio.

1. Focal Length. I also think focal length is still one of the most overlooked issue by newbies, despite conversations about the 38mm "problem" which have been coming up regularly since as early as 1998 as far as I remember participating. Using something around 50-80mm for body shots and 85-135mm for headshots will drastically improve a lot of poser work.

2a. Shadow Maps. I don't know if this has come up before, or recently, but shadows deserve some attention. Firstly, be sure to increase the size of your lights' shadow maps. 256px is the default, and it produces shadows with nasty looking edges from lack of resolution. Make the shadow maps at least as big as your canvas dimensions.

2b. Shadow Intensities. Adjust shadow intensities. Don't make all your lights cast shadows of 100% darkness unless you are after hard shadows. For realism, I don't believe in turning spot light shadows off entirely (you can't do this in the real world), but you can lessen the intensity of spot light shadows to give the impression of more diffuse lighting.

3. Spot lights - Use them. Real photo studios mix spot lights with diffused "fill" lighting, and so should you! Consult any of the hundreds of photographic lighting tutorials on the internet.. most of what applies to real-world lighting also applies to 3D program virtual lighting.

4. Posette Lastly, use of the default P4 woman "Posette" with flat-yellow or red plastic-looking ponytail hair is also one of those things that makes a render instantly identifiable as newbie work. Also, a lot of times when you see work in magazines that is identifiable as poser, it's because of this.

Hope this helps!

-Adam