Here’s how to make a nifty painted floorcloth (i.e., canvas rug)… Tack or staple (close together - about 2 inches) the edges of your close-woven canvas to a sturdy frame to work on for greater ease. If you need to sew two pieces of canvas together, use waxed thread or sailmaker’s twine - and use an overlapping stitch for greater strength. Open out the seam, press it with an iron, and glue the selvedges (with PVA-based "milky" glue that stays flexible when dry) flat against the back of the canvas.

For a good painting surface that will stay cleaner when walked on, prime the canvas with acrylic primer or synthetic gesso (more expensive). For best results, top this with a layer of flat oil-based paint in any suitable background color. Use a fairly large brush, and stroke the paint on evenly to the edges. (The edges will be turned under and flattened down, so don’t worry about a little wrinkling there.) The layers will go on unevenly at first as the canvas soaks up the paint - later coats will go more quickly and smooth things out. After the third coat, rub it down lightly with medium sandpaper, then wipe it with a cloth - and do this after each new coat. (This step is important - it helps keep the floorcloth smoother and more supple.) The more coats of primer (plan on at least 3-4), the tougher - and smoother - the floorcloth. (It’s a good idea to protect the underside with a coat or two as well.)

On to the designs... Acrylic paints are the easiest to use (cheap and dry quickly), but artists’ oils are fine too, if you have the time to wait.  You can use a pencil or colored chalk to lightly trace a design before you paint it. You can also stencil one or more layers of paint (just be sure to use a heavy enough pigmented paint to cover the last layer). Use whatever design/technique you like - sponging, spattering, stamping, rolling, anything. Remember to allow for folding under the edges...

As with seams, fold, press, and glue flat. Some people apply a slightly tinted glaze to soften harsh colors in the finished painting and make it look older. When you’re satisfied with your design, use two coats of polyurethane varnish thinned with 1/4 mineral spirits ("white spirit" solvent) to finish it off. Add another couple of coats of spirits thinned 1/4 with varnish. Use a large brush and stroke it on thinly and quickly. (Allow each coat to dry at least half a day - the stuff continues to harden up even after it feels dry much sooner than that.)

And a final word of caution: Don’t fold it! - the surface with crack and its integrity will be weakened.