There are several really good tutorials on how to do this out there, but I found most of them to be a bit too involved. They had you imagining spheres of vary degrees of intensity, you were supposed to wet blend and highlight, and it just seemed a bit much to me - I was just wanting to try something simple and see how it looks.
Since I wanted to keep it simple I decided to use the simplest of all miniature painting techniques - drybrushing. For this experiment I dug some terminators out of the bits box and primed them black. From there I applied three different layers of paint using the large GW Dry Brush.
I started with Dark Angles Green. I put this down in a fairly large area. I then went over that with a slightly less thorough coat of Goblin Green. To top it off I used an even lighter coat of Scorpion Green.
This model took me less than five minutes to do. This process was really quick and it did exactly what I wanted it to do - the model looks like it has light shining on it. Where the method falls apart on this model is that it is not obvious that it is supposed to be coming from the Storm Shield, Thunder Hammer, and the models eyes. I think I was just trying to do too much.
Never the less I did learn a lot from this exercise. I highly recommend digging a spare model out of the bits box and trying this over a pure white or black base coat. You could use any color that has a strong progression - red to orange or yellow, blues working up to Ice Blue, greens like I did here, or maybe even some more exotic color scheme like grays or purples. The main thing is to just try it out - keep it simple and progress to more complicated and involved methods after you get this method down.