If you're just getting into modeling photography, here's a checklist of things to work on and working tips:
Even skin tones - no blotches of random light across your model
No Raccoon eyes - when light is from overhead, eye sockets tend to go dark
Fill light - get a big honking flash or big reflector and learn to use it to even out skin tones, fill shadows, but not over do it
Simplify your backgrounds
USE the background - make sure each element of the background is there for a reason. Try this - take 10 "finished" photos of different subjects or same subject in different places, but ignore the subject and make sure the background is perfect in each shot. This isn't for your portfolio - this is learning. Once you know how to frame using the background, go back to working with the subject.
Learn to use DOF (Depth of field) to isolate your model
Make sure focus is tack sharp on their eyes
Create "concept" photo shoots - create a story to work by so that wardrobe, makeup, posing and shooting style all speak the same language
Work on getting really good eye contact with your models - the eyes should have an intensity, not just be staring sort of towards the camera
Always work with at least a good makeup artist, and ideally also with a stylist and a couple of assistants to move your flash/reflectors around and hand you the donut when you need it.
Rules are made to be broken (except those last two) - but not till you know the rules so well you don't think about them any more.
You should also be looking at top notch photographer's work and comparing what you get to the standards they set. When you see a shortcoming, make changes to your work. Don't copy their "style" - copy their quality.
BTW - this is advice I'd give to any photographer trying to improve.
