Use a square piece of paper 3"x3" works well.
Draw a line from one corner to the next. You will be cutting along this line so make it interesting but not too complicated.
Draw a second line connecting one corner to the next. The two lines should not intersect.
Get a pair of scissors.
Carefully cut along the lines.
Slide the cut out pieces directly across.
Get some tape.
Tape the pieces together. Make sure there are no gaps between the paper and that the corners line up.
Get a pencil and your sketchbook and trace your shape.
Check to make sure it tessellates!
Check every side
Did it work?
Add details! You may need to turn the image around a few times before it inspires you.
Now it's time for your good copy. Trace your shape until it fills the entire page. It's okay if lines go off the edge of the paper. Draw in the details and add color.