Start by measuring and cutting a 11.5 in x 29 in piece of canvas.
If you're painting your own design on the canvas or dyeing the canvas a solid color, now is the time to complete that process.
You can use fabric paint, a little water to thin out the paint if desired, and a paint brush.
OR you can dye the entire piece of canvas using this technique: how to dye natural fibers. Wait for it to completely dry before moving onto the next step.