Start by drawing the main shapes that will make up your pattern. You can use an image as a template to trace over if you want. I found an image of a leopard print.

When it looks like you have a good chunk of your pattern going, you can begin defining its outer edges.

I started at the top. It looks like the three shapes in red will form the top outer edge of my pattern tile.

Identify the shapes that form the top of your pattern and copy then paste them to the bottom outer edge of your pattern.

Next, I looked  at the left outer edge. These couple of pieces in red make up the left edge of my pattern.

Identify the shapes that form the left outer edge of your pattern and copy then paste them over to the right outer edge.

In order for Illustrator to create a repeating tile for you, it needs you to turn in your pattern in the form of a rectangle. Now’s a good time to establish that rectangle. Your pattern isn’t quite ready to be cropped and saved at this stage but drawing the cropping rectangle now will give you a better idea of any empty gaps happening inside your pattern so you can continue fleshing it out. (Apologizing now for the extreme usage of the pseudo term, “cropping rectangle.” I don’t know what the technical term for it is or if there is one but it appears A LOT throughout the rest of this tutorial just because I tried to be the least amount of confusing about things. If it ends up confusing you more, I’m genuinely sorry about that.)

Draw your cropping rectangle with a stroke and no fill. It doesn’t matter what color or weight stroke you use since you’ll turn off stroke before saving the tile. For now, pick a stroke that helps you clearly see where the outer borders of your crop are in relation to your pattern.

Where the heck do you place this rectangle and how big or small is it supposed to be? 

The top of your cropping rectangle should dissect the shapes along the top edge of your pattern. Remember copying and pasting these shapes to the bottom of your pattern? The bottom of your cropping rectangle should dissect those same exact shapes along the bottom edge of your pattern. Eyeball it so it looks like they’re being dissected in the same spot for now. Basically, if you dissect a shape at the top, you need to dissect the same shape in the same spot at the bottom.

Determine the left and right borders of your cropping rectangle in the same way. Drag the left edge of your rectangle so it dissects the shapes along the left border of your pattern. We copied and pasted these shapes over to the right edge of our pattern earlier. Roughly dissect those same exact shapes on the right with the right edge of your cropping rectangle.

Organic patterns tile seamlessly when cutoff shapes along all four sides align with their counterparts contained in the next tile. If I cut half a shape out of my tile on the left, the other half of that shape needs to be included in the tile on the right. That way the two halves will join when two pattern tiles line up and create a whole shape. This is one of those things that makes more sense once you save a couple of jacked up tiles. If you save a pattern tile and shapes aren’t matching up, your cropping rectangle may need to be adjusted so it’s dissecting the shapes along your pattern borders in a way that they will perfectly complete each other top to bottom, left to right, once tiled.

So before we continue fleshing out our pattern design, let’s ensure that our cropping rectangle is perfectly situated to crop a tile that matches our shapes up seamlessly.

There’s probably a more precise way to do this but here’s what works for me: Starting at the top border of your rectangle, zoom in close and draw a rectangle the height of one of your dissected shapes. I made my rectangle transparent so I could see my pattern shapes underneath. Basically, I use this new rectangle as a crude measuring tool to determine if the dissected shape’s counterpart at the bottom of my pattern is being dissected in the same exact spot.

Drag your measuring rectangle over the same shape that’s sitting at the bottom edge of your pattern so that it touches the bottom border of your cropping rectangle. If the height that’s outside the top border of your cropping rectangle doesn’t match the height that’s inside the bottom border of your cropping rectangle, adjust its borders until they do match up. Do the same for your left and right edges.

Again, this method is imprecise and you may save a tile only to see that your pattern is off by a few points here and there and your cropping rectangle needs to be fiddled with. This usually works for me pretty well though and it isn’t a huge deal to go back and adjust for a new tile if needed since saving pattern tiles in Illustrator is very easy. It’s constructing the tile that requires the bulk of your efforts.

Now that your cropping rectangle is the right size and situated properly, you can continue fleshing out and brushing up your pattern tile. You may notice shapes that land squarely outside the borders of your cropping rectangle. If no part of those shapes sits inside your cropping rectangle, you can go ahead and delete them. This usually means they’re represented somewhere within your tile already.

Draw more shapes to fill in your pattern if you see any unwanted gaps. There were gaps near the top and bottom borders of my pattern. I drew new filler shapes that ended up being dissected by my cropping rectangle so I copied them down to the bottom to ensure that they’d look whole after tiling. Be sure to place any repeating shapes in the same exact position relative to your cropping rectangle’s borders.

Copy over any new shapes from your left pattern border over to the right, again positioning them so they’re in the same exact spot relative to your cropping rectangle.

When you’re done filling out the shapes in your pattern tile, you can start applying things like color and texture or add accenting details. (If you haven’t already. You can apply those things from the beginning, I just didn’t in this tutorial.)

Here’s mine after applying a background color, artsy strokes, fill colors and some smaller detail flecks. I hid my cropping rectangle to get a better look at things during this part.

Applying Multiple Colors and Other Effects

I wanted to add other colors to my pattern. Here’s a couple of notes about choosing which shapes to color or treat differently from the rest of your pattern (i.e., using filters, textures, etc.):

• If you color shapes that sit partly outside the borders of your pattern tile (any shape being dissected by your cropping rectangle), make sure you give their counterpart the same color. In my pattern, the corner “kidney bean” shapes all need to be teal since pieces of them line up to form the whole kidney bean shape once tiled. I forgot this at first and saved a wonky tile with corner kidney beans made of disparate sections of both teal and orange.

• How you distribute your color within the pattern effects the movement in the pattern once tiled. In the left example below, I applied the teal color to shapes that are in the same “column” visually. This created very apparent vertical lines of teal as the pattern repeated. In the right example, I limited the number of shapes I made teal and applied the color to shapes that didn’t line up as closely in rows or columns. This created teal shapes that flow more wave-like. Since I want this pattern to have an organic movement to it, the affect on the right works better for me but experiment to achieve the look you’re going for.

Now we save the tile.

This is the easy part. Here’s my cropping rectangle again. Select your’s and set it to have no fill and no stroke. Then send it to back. Select everything that you want included in your pattern (hide or delete anything you don’t want to be a part of it).

Go to Edit > Define Pattern and click. Name your swatch. Anything. Click OK.

Your custom pattern tile is now in your swatches palette! If you don’t see it, check the very end row of your color swatches. Make any shape and fill it with your pattern tile to test it out. You can save this Illustrator document and edit and create new versions of your pattern ad infinitum. Enjoy!