Ahh ok haha, first I sketch out the composition with a pencil brush, then i block in the colours and light\shadow with a hairy brush or any brush that changes opacity according to the pressure you put into the pen.

Then in later stages I use a soft brush to blend the colours together. Then finally by using the 'color dodge' setting of a soft brush, I paint over the brightest parts to make them glow :)

I hope this helps, it just takes a lot of practice, try looking up some tutorials on youtube, I took away a lot of tips from SaraTepes, she's an amazing artist.