Weights are not something or someone you should play games with. They are your best friend in the gym, but also your obstacle in the gym. If you are polite to them, they will be even politer.
Do not start an exercise or a workout machine with high level of intensity just to prove a point among your friends or to impress a girl working out next to you. The weights will hit back. How?! – Definitely not in the nose, NO; but directly to your weakest muscles thus initiating an injury.
As I said before, be polite to them. Start an exercise with small weights or level, and then if you feel strong enough to increase, do it; if not, overcome the starting level and then increase when feel ready. A normal weight gap between sets is 10 kg (22lb) for barbell exercise (that’s 5kg (11lb) on each side); for a dumbbell exercise its around 4-5 kg. If you feel 5 kg is too much, then make a 2, 5 kg gap. But make sure you work with a 5 kg gap as you progress further.
When you place a weight on a barbell, do it with caution (especially with heavier weights). Improper handling with barbell weights can twist your wrists while placing them on the sides. Usually, 5 kg (11 lb) are handled with one arm, that’s ok; but for safety reasons place a 5kg weight on a barbell with two hands. All other weights should be placed with two hands. Don’t act cool and handle the weights with one arm.
Always return the weights back to their stationary racks. A clean Gym is a Safe Gym. People trip from weights on the floor all the time. Imagine what can happen if you trip on a weight and land on a workout machine the wrong way! Every gym should have a sign: SAFETY FIRST!