Note: (credited to benihimecosplay) Using sharpie to draw in the shapes will cause it to bleed onto the fabric.
I forgot to mention, but do follow the instructions of your paint and set it properly. It usually means ironing over it after it dries. And if you do screw up, you can dab at the paint with your wet towel before it dries and hopes that it'll be taken off.
This tutorial is pretty straightforward, but the most important thing here was the usage of materials. Most people use contact paper or oaktag/cardboard. But I find that these materials either curl up or has the tendency to move around. Freezer paper sticks and not leave any residue.
The brushes you use is also important. Sponge/foam brushes makes the paint even, while paint brushes tends to make it streaky. Spouncers are usually the best because of its round shape. They might be a bit expensive but keep washing them out before the paint dries and reusing them until they die.
For an idea about how to do a more intricate design, or just how the process goes, I recommend watching a time-lapse I done a long time ago. Go to this link: [link]
Don't follow the materials I mentioned there anymore. Screenprinting ink has a tendency to crack too, fabric paint like Tulips (not the 3D ones) are the best to use.