Step 1: Materials
A piece of paper (scrap, colored, anything, an it doesn't have to big either)
Scissors, for the obvious reason of cutting paper. You can do the fold-and-rip method if you wish.
Step 2: Cut Out a Rectangle
The measurement doesn't really matter, but it must be a rectangle, not square. If you want to be sure, the length of the side should be somewhere between 2 to 3 times the length of the width.
Step 3: Fold in Half
Step 4: Fold in Fours
These folds should be in the opposite direction to the fold you made for the halves.
Step 5: Cut a Triangle
In the photo, the triangle is colored in with black for your convenience to see.
Step 6: Blow
The picture shows in red the area your lips should be.
Hope this helped! :)