Create a stand for lightweight cutouts made from foam core, cardboard or 1/8-inch plywood by cutting a 15-inch square of 3/4-inch plywood with a miter saw.
Cut a 15-inch length of 2-by-4 lumber with a miter (sometimes called "chop") saw and screw it to the square along one of the 2-inch edges, about 2 inches from one side of the square.
Paint the entire piece black or the color of your stage floor, if it is something other than black. When the paint is dry, staple the prop cutout to the 2-by-4, facing the end with only 2 inches showing, using 3/4-inch staples.
Set the prop in place on its floor plate and weigh it down with a stage weight or sandbag. This method works well for low cutout bushes and other ground rows that are lightweight and no more than 3 feet high.
Make heavier props stand upright by cutting three lengths of 2-by-4: one at 2/3 the prop's height ("A"); one at 1/4 the prop's height ("B"); and one that is the square root of length A squared plus length B squared ("C") -- it's OK to round to the nearest inch.
Attach board "A" to board "B" using two screws driven through the base of "A," when held upright, into the end of "B."
Trim one end of board "C" to a 30-degree angle and the other end to a 60-degree angle, both angling toward the same face of the board. Use board "C" to complete the triangle begun by "A" and "B," and screw it in place. A little bit of boards "A" and "B" may stick out on the ends -- this is fine.
Cut a piece of lumber half the length of "B" with a 30-degree angle in one end and screw it in as a brace inside the middle of the triangle.
Screw the prop into the face of board "A" and screw the stand, known as a "jack" or "stile," into the floor to secure it. If your prop has a wide enough base that the jack seems sturdy without screwing it down, you may choose to simply weigh it down with sandbags, especially if it is only on stage for a short time.