I wasn't really sure how to go about making a tessellation at first, so I began by making random shapes out of rectangles and triangles and other shapes on graph paper. I would then tweak those shapes to try to get them to fit together. I ended up getting something a bit like this:
I later found a website that showed different methods for making tessellations, and I chose one of them to loosely follow for mine (here is the link to the page: http://www.tessellations.org/methods-tracing-paper-0.shtml). I didn't follow all of the steps exactly, and only used one sheet of paper to sketch out my tessellation, but it did help a lot to use a grid with even rectangles for more structure. I turned the sides of those rectangles into squiggly lines and tried to to think of what they looked like--like when you try to figure out what clouds look like. I thought they looked slightly like disproportionate pigs, so I decided to go with it. I tweaked the shapes to get them to look more pig-like. Here is my first draft:
As you can see, the pigs are roughly the same shape and size, but they are still not completely equal. I had to keep adjusting the back of the pig so that the front would fit, and same for the top and bottom. The pigs went through many changes until they fit together just right:
^The final pig is on the bottom. To get my final tessellation, I traced and re-traced that pig on a grid, added details, and... voila! Pigs!