Smith Machine Bench Press
Starting position:
Prepare the appropriate weight matching your fitness level and training type. Lay on the bench so that your eye level is right below the Smith machine bar. Grab the bar using an overhand grip so that elbows are at about 90 degrees in the lower position (the position when elbows and arms are at the same level). Feet are fixed on the floor.
Exercise:
From the starting position lower the barbell down until the bar touches your chest and return it back to the starting position. Inhale while making the downwards motion and exhale with the upward motion. Fix the thoracic muscles and the position of your pelvis to avoid lumbodorsal swayback upon resistance. Elbows go apart from each other.
Note:
Do not overestimate your capacities when choosing the weight. Watch for correct position of your hands and avoid excessive dorsal flexing of the wrists. Avoid lumbodorsal swayback when overcoming the resistance, your chest and whole torso must be firm and fixed throughout.
Recommendation:
It is better to exercise with assistance of a trainer (spotter) when using heavier weights. The number of repetitions depends on your type of training.
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The Smith machine is actually a supporting mechanism for bench press and other potentially dangerous exercises with barbell. The machine is designed so as to replace the spotter.
It should be noted that Smith machine is forcing you into movement that is both isolated and less natural than regular bench press. These are significant disadvantages.