Here I started with purple and used different hand pressures to apply it. Some places I wanted it more opaque and other places ...not so much. The picture above, I already started to apply my third color.
There aren't any right or wrong ways to do this, so just go with it and have fun!
I also used a small eyeliner makeup brush to add the bigger star bursts, you don't have to do this, but it's a neat little add on.
Wait for your galaxy master piece to dry and then gently remove the masking tape from the glass. If some of it comes off, no worries, just sponge on a little more black paint.