I was playing Space Marine the other day, and I was interested in the way they handle their smoke textures. The textures aren't animated as far as I can tell, and manage to get a lot of mileage without needing too high of a particle count.
I decided to try painting a smoke texture similar to the ones they used.
First I painted a brush to use to make the body of the smoke.
I made it out of a gradient circle brush and the smudge tool. I set it to use a bit of scatter, random angle and size, and a dual brush with a gradient circle to help unify the edges while painting.
I painted the general shape of the smoke with the brush.
|Good alpha map...|
|...Gives good results!|
|Bad alpha map...|
|... Gives bad results :(|