Shoulders are one of the most worked/used muscles in your body. Your shoulders along with your triceps are what actually make your arms looked toned, fit, or big if you’re looking for volume. Whether you’re working out your chest, back, or arms you’re almost always using your shoulders in the exercise.
Because of the constant use coupled with the fragile ball joint that is connected to your shoulders, it’s important that you’re doing the correct exercises and not over fatiguing your shoulder muscles. If you’re starting out, go for lower weight, higher rep workouts rather than higher weight lower rep workouts. As you get comfortable with the movements feel free to increase the weight you’re lifting.
For the best outcome during your shoulder toning exercise, hit multiple angles and parts of your shoulder (front, back, deltoids, etc) as well as high volume medium to high weight (again as you get comfortable with the workouts) repetitions. You really want to feel a good pump during the workout to maximize your time and effort. Use free weights (dumbbells, barbells, EZ bars) when you can as they’re more challenging and will give you a more full workout. Dumbbells especially will give you an even workout as to not “cheat” by using your dominant shoulder more than the other.