Photography literally means 'Light writing' or as I like to think of it, painting with light.
So, it goes without saying then that light is the paint on your palette if you're wanting to create works of art. There are many ways to create different moods with light and they don't have to involve lots of expensive equipment either.
Here's a shot I took at a fashion shoot I did a for a models portfolio.
The ambient light was mixed tungsten and day light, the time of day was early evening during Spring so there was fading light outside.
To create this atmosphere, I used a Canon 430 EXII on a light stand with a couple of pocket wizards and a honeycomb over the flash.
As you can see the direction of the flash head was quite high, illuminating the face and chest, then falling away naturally towards the legs.
The light was at half power and the shutter was 1/125 on my trusty 'nifty fifty' lens at F5 to keep the subjects face sharp and throw the background out of focus.
If you're really on a budget then you can create the same effect with drinking straws, just bunch them together with tape and attach them to the front of your flash, however, if you're on a paid shoot, it looks better if you have invested in a proper attachment!