Use a roller on the top, flat side of indoor or outdoor bleachers. If your roller has a long handle, you can stand in one spot and paint multiple bleacher levels without moving. Once you've covered a wide area, move up or down the bleachers and continue painting.
Stand under the bleachers to paint the bottom side. Using a roller with an especially long handle or a telescoping handle, you can stand under the bleachers and paint all the way up. If you find that your handle isn't long enough, use a ladder to move up as the bleachers rise.
Buy a small roller for the sides of the individual bleacher planks. Most bleachers are relatively thin, so a small roller is best for working with limited space. Be sure to wait for the paint to dry thoroughly on the top and bottom sides of the bleachers if you paint the thin sides last.
Purchase a heavy-duty paint made specifically for the environment you're working in. If you're painting outdoor bleachers, a paint that resists weather is crucial. If you're painting indoor bleachers choose an appropriate mix that won't overwhelm you with fumes.