Cut your fabric two inches longer than your blinds, width and length. Since one of my blinds was 22 1/2 inches x 52 inches, I cut my fabric to 24 1/2 inches x 54 inches. The reason for this is so you can fold all the edges over. You may want to iron a crease on the edges to make it easier.
Use fabric glue to create your hems all around. You can also sew this if you want a more tailored look. You may also use Heat and Bond, but trust me it’s more work and you can't tell the difference between that and fabric glue.