BIRDS by Stephen
Birds are very possibly the most popular theme for tessellations. Escher did dozens. Why? Well, they're colorful, flexible, and come in an amazing variety of shapes.
Stephen's tessellation has almost all the right qualities of a good tessellation. He used a tutorial, but dared to be original. It has perfect repetition of the "tiles" (in this case, bird shapes). It has contrasting colors, so you know where one bird ends and the next begins. The fit is snug, with uniformly thin lines marking the space between "tiles". There are no gaps or overlaps between the "tiles" (birds). :^)
If I could make only one change, it would be that after stephen made the bird shape, he would used the eraser side of the pencil and the pointy end to improve the bird shape 'til it becomes a more birdlike recognizable outline. Later I'll be writing a tutorial about that tweaking process, because so many first-timers could make their tessellations even better.