Front dumbbell raises are the best exercise to isolate the anterior deltoid head (the front of the shoulder).
The shoulder muscle consisted of three heads: front (anterior), side (lateral) and back (posterior). Although the front delts get a lot of work through compound exercises like bench presses and push ups, you might want to isolate the muscle to fatigue it completely, resulting in more muscle growth. Just don't forget to work the lateral and posterior heads as well for a balanced shoulder.
Use a light weight. This is an isolation exercise, that works a very small muscle - only one of three heads of the shoulders. Don't expect to lift nearly as much as you can shoulder press. Using too much weight will end you up with a bad form and other muscles taking over the movement, making this exercise less effective and increasing the risk of injury. It is best to use low weight and high reps (between 10 to 15).
Keep your back still. A common mistake is to arch the back while lifting resulting in a bouncing movement of your torso back and forth. This removes the pressure off your delts to the bigger back muscles. This kind of movement might indicate you are using too much weight. Keep your torso still, and reduce the weight if necessary.
Don't allow the weights to touch your body at the bottom of the movement. Keeping the weight a little far from your body will keep the tension on your delts throughout the entire range of motion.
Lower the weight slowly. Don't just drop them by your sides, but lower them in a slow, controlled manner. Lowering them slowly will keep the tension on your delts, leading to more muscle growth. It will also prevent you from using momentum.
Don’t go beyond parallel when you’re raising the weights. This will engage your traps instead of the delts, and it puts unnecessary stress on your shoulders and might lead to injury.
Make sure to keep the arms straight but not locking the elbow. If the arms start to bend over its time to use a lighter weight. Allow a slight bend in your elbow, this will remove triceps involvement, and reduce the stress on the joints.