for this, you will need:
-Regular sized brush
-Detail/ultra detail brush (depending on how big you want the runes)
-Colours (at your discretion, but you will need a dark tone, a medium tone, and white. You can just keep adding more white if you only have one shade in most cases)
First off, paint on the basic shape of the runes. Ideas for runes can be found in various Chaos texts (such as the previous two editions of the Fantasy Warriors of Chaos books). It's better if you paint them slightly thicker than what you want, since this will be the final, weakest stage of the glow. Feather/blend them on the outer edges.
Next, paint on a 50/50 mix of your dark and mid tones. Here, I'm using Caliban Green and Moot Green. Paint this on so that some of the wider painted previous colour shows around the edges.
Now move onto your smaller brush. Add a pure mid tone layer.
Paint on a 25/75 mix of white to mid tone in the centre of the runes. Again, make sure to leave some of the previous colour. follow this up with a 50/50 mix.
To finish off, use a 75/25 mix of white and mid tone, and paint very thin lines in the middle. Add white to select areas of the rune (mainly the exact centre).
And there you have it, glowing runes to scare non-believers and bound your daemons to engines of destruction. If you fancy a go and like the results, share them on the Facebook page.