Place a chair 3 feet away from a wall, facing parallel to the wall. The chair should not have arms, and be sturdy enough to take a plank being rested on it. Use one that you don't mind being tarnished slightly, as the plank may cause wear and tear.
Rest the plank of wood on the chair, so that the plank runs from the edge of the chair down to the corner of the wall and the floor. The plank should be at about a 45-degree angle. Adjust the chair until this is the case, by moving it further or closer to the wall. The plank should extend approximately a foot over the edge of the chair.
Kneel against the side of the chair opposite to where the plank sits, using your knees to hold the chair still. Use the cushions or pillows under your knees for comfort. Hold two dumbbells or a barbell so your arms, hands facing up, are straight against the plank. Raise your hands and forearms, curling the weight up towards you. When you have brought the weight up, lower to the starting position. This is one rep. Three sets of eight reps is the optimum number for a beginner looking to improve muscle mass.