1- Sit straight on seat or bench with barbell rack, hold the barbell with a wide overhand grip resting it across the upper chest.
2- Inhale, push the barbell up straight along your arms length, keep your back as steady as possible.
3- Exhale at the end of movement, slowly lower the weight down to its starting point across upper chest, repeat until you finish the set.
4- Carefully return the weight to its place on the rack.
Tips and Advises:
1- Make sure that your back remains stationary though out the exercise and move only arms.
2- To avoid injury, only lower the bar as long as your shoulder's flexibility allow you to, don't over do it.
3- Wider bar grip with elbows out isolates anterior and middle delts.
4- A narrow grip with elbow forward isolates anterior delts and clavicular head of pictoralis major.
5- Performing shorter reps (not withing the whole range of motion(Increases stress on deltoid muscles)..
Variation:
1- You can perform the same exercise while standing, this version is lighter, since it allows you to cheat the weight up with body momentum.
2- Seated Behind-The-Neck Press.