1- Sit straight on seat or bench with barbell rack, hold the barbell across the back of your neck with a wide overhand grip.
2- Push the barbell up straight along your arms length, keep your back as steady as possible.
3- Slowly lower the weight down to its starting point behind your neck, 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 decreases triceps work, but increases shoulder chance of injury.
4- 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 Barbell Front Press