Select the appropriate weight matching your type of training and your fitness level. Lie down on an incline bench placed underneath a Smith machine and secure your legs at the end. Set your bench so that the bar is straight over your chest. Grab the barbell with your palms facing forward (thumbs turned inward) using a medium grip creating a 90-degree angle in the lower position (when elbows and shoulders are parallel). Place your feet firmly on the floor.
Come down slowly until you feel the bar on your lower chest and then go back to your starting position. Breathe in as you go down and breathe out as you go up. Make sure your back and torso are straight to avoid lumbar lordosis (straining your lower back). Your elbows point outwards.
Do not over overrate your capacity while selecting the appropriate weight. Make sure your hands are in the correct position and avoid extensive dorsal flexion in your wrists. Make sure you avoid straining your lower back; both your chest and entire torso must be straight and firm all the way through.
Choose the number of repetitions to match your training type.
Decline barbell bench press is thought to strengthen and build the lower part of pectoralis (chest) muscle.
All the precautions you should take when doing regular bench press apply. The technique is also similar except for the arching. The back is firm on the bench.
Interestingly, a study by Barnett and colleagues from 1995 found that bench press on a flat bench activates more lower-pectoralis muscle fibers than decline bench press. Therefore, the usefulness of decline bench press is rather questionable.