As promised here are a few pointers on using polarising filters. Firstly there are two types of polarising filters. If you use autofocus as most of us do then you'll want a circular polarising filter.
The first important tip for using a polariser. It doesn't work properly with other filters on your camera; so get those skylight and UV filters off your lens before you put on your polariser. This will also help remove the chance of vignetting which is a distinct possibility when you use wide angles.
So what do you use a polariser for. The two main purposes are to darken skies and to remove reflections.
Firstly darkening skies, which neatly brings me to the second important tip. Polarising filters only really work when used at 90 degrees to the sun. So if you stand facing the sun and stick your arm out from your side, that's the ideal direction to point your lens if you want to darken the sky. If you use a polariser and point your lens in the direction of the sun or with the sun behind you, you may as well not bother.
Another thing to watch out for is using a polarising filter with an extreme wide angle. Because you've got so much sky in the shot your polariser will work differently across the frame which means part of the sky will be darker and part lighter, which can be quite unattractive.
As mentioned polarising filters are also used to remove reflections. These could be in a window, on water or even on shiny foliage. Whenever you're photographing a refelctive surface the polarising filter is well worth bearing in mind.
An added benefit of polarising filters, when used correctly is that they tend to increase colour saturation.
Polarising filters are undoubtably extremely useful and an essential part of the photographers' kit. What's more this is one filter which digital manipulation simply can't imitate as it has a profound effect on the light that hits your sensor.
Hope you have fun out there and remember my tips above. Here's an extra tip before I go. Always take one shot with the filter and another without so you can compare the results. It's the best way to learn by seeing the effect your filter has had on the end result.