You are using 50mm lens with polarizer filter for what? You can't see the difference until you take scenery photo with sky and water, or you shoot your model through the glass.

From the beginning all the user advise you not too over-depending on the tools you have but you insisted that your gears are poor. Please stop depend on your gear, as your major problem comes from your skill, the way you compose, the way you post-process and the way you convey your idea through the picture. Please bear in mind on this.

Anyhow, you have improved slightly, at least now you frame the model correctly, with the rule. At the current stage, you're good to stick to the rule until you have better sense to break the rule in portraiture shooting.

Don't buy or use something that you don't know what is the usage. To give you better image, read this:

http://en.wikipedia.org/wiki/Polarization_(waves)

See how it does. There is certain light ray (vertical) will be filtered through polarization. So when it comes to light ray reflection, it will be filtered thus, what we can see is "clean" image, without ray reflection disturbance. So what to do with your model? Your model does reflect light? What the...

Do more research, as I said, don't depend on your gear too much. It's about creativity. You can have good picture with compact camera I dare you. The difference of that is just DSLR has more customisation.