Lay underneath bench with bar up high, feet on the ground back stiff. Pull up to bar.
Or
Set up a barbell on a power rack three to four feet above the floor. Lie under the bar and grab it with a shoulder-width grip. Hang at arm's length from the bar with your body in a straight line from your ankles to your shoulders
Bar, Bench, Power Rack
Wide Grip, Close Grip, Reverse Grip