FIGHT ME.

Well, For the clouds i used the cloud brush. I downloaded a version of sai that had it loaded with nice brushes and textures. I wish i could give you a link, but i don’t even remember how i found it. I do know that it was a pain cause i had to download another program to open it.

You most likely don’t have this version. I have the settings you could play with.

As for the sky, i had a dark color blended with a lighter one(Or light color blended with a darker it doesn’t matter)

Add stars. I used mostly white, and yellow for the colors. Blue, red and a few others were added in after for interest. I also used the pen setting. It’s clean and makes the stars look really sharp.
I got lazy half way through the paper bag pic and copy and pasted clusters of stars and just messed with rotation.

Clouds. Use another color than white. I used blue here.

Ta-da