How to Perform Incline Dumbbell Curls
The bicep brachii comprises roughly one-third of the upper arm and is comprised of the long and short heads. The brachialis, also referred to as the side arm or lower bicep is commonly considered part of the bicep muscle group even though it's technically different.
The biceps are primarily built through pulling movements such as chin-ups and elbow flexion exercises such as curls. Most bicep movements are performed in vertical plane although the torso angle may also be slightly backward (e.g. incline dumbbell curls) or forward (e.g. concentration curl) depending on the exercise. Whether you're a top-tier athlete or weekend warrior a beastly set of biceps will set your physique apart from the rest.
The incline dumbbell curl is an isolation pull exercise targeting the biceps brachii, which is comprised of the short and long heads. The brachioradialis (upper-outer forearm) and brachialis (lower bicep) act as supporting muscle groups during this movement.1
Supporting muscle groups assist the target muscle group in completing the movement. The anterior or front deltoid and wrist flexors act as stabilizers during this exercise.  Stabilizer muscles help maintain a posture or fixate a joint by contracting without significantly moving. 
The backward incline of your torso dramatically increases the difficulty of curling the dumbbell by placing the bicep in a mechanically less advantageous position.
MTS Nutrition CEO Marc Lobliner shows your to perform incline dumbbell curls.
How to Perform the Incline Dumbbell CurlApproach a free-standing adjustable bench, ensure you've got plenty of room on all sides of it, and adjust the back pad so that it creates a 45-60o angle with the ground. You don't need to use a protractor and measure but it should be somewhere in between vertical and horizontal.
As the back pad angle increases and becomes more upright it will feel and look more like a traditional dumbbell curl. Adjust the seat pad so that you're comfortable and not sliding off the bench.
Now go to the dumbbell rack and select the appropriate working weight. If you've previously performed traditional dumbbell curls then be prepared to start with a lower initial working weight. Select two dumbbells of equal weight; don't lift 20lbs with your left arm and 30lbs with your right arm.
Uneven loading won't improve your gains and will likely lead to an injury. If this is your first time performing the exercise then pick a conservative weight that you can safely lift for 8 to 12 repetitions.
Once you've selected the appropriate working weight grasp the dumbbells, pick them up, sit down on the seat pad, and let the dumbbells hang to your sides. Your arms should be straight but not hyperextended, the chest should be up, shoulder blades should be retracted, and glutes should be in contact with the seat pad.
Once you're in position take a neutral grip (palms facing towards each other) using a traditional (thumb wrapped around the fingers) or false grip (thumbs wrapped around the same side as the fingers). This is your starting position. You can also start with a supinated grip (palms facing away from you) instead of a neutral grip.
After setting your starting position take a deep breath, brace your abdominals, squeeze the dumbbells as hard as possible and begin pulling your hands towards your shoulder. During this arc motion, your elbows and upper arms should remain in a fixed location. Do not allow the upper arms or elbows to drift out of place; doing so will take the stress off the target muscle groups.
Continue curling the dumbbell until your forearms are in between parallel and perpendicular with the ground. The precise top position will vary with the individual, depending largely on your upper arm strength, form, and shoulder flexibility. While some trainees prefer to curl the dumbbell until the forearm is perpendicular with the ground, this may require your elbow to drift forward or shoulder to roll-in or raise.
Curl the weight towards your shoulder as much as possible, stopping just before your elbows and shoulders change positions. This cue will maximize engagement of the target muscle groups. Continue squeezing the dumbbells and flexing the biceps, holding at the top position for 1 to 5 seconds.
Once you've held the dumbbells at the top of the movement for the desired duration lower the dumbbells in a slow and controlled motion back to the starting position. The movement pattern for the lowering portion should be the exact reverse of the pulling portion. Complete for the desired number of repetitions.
You can perform this movement curling one dumbbell at a time (alternating) or curl both dumbbells at the same time (simultaneous). Some lifters choose to exhale while curling the dumbbells, at the top of each rep, or in between in each repetition. Choose a breathing pattern that feels the most natural and comfortable for you.
This exercise can be performed using straight sets, pre-exhaust sets, drop sets, rest-pause sets, supersets, trisets, giant sets, paused reps, or slow negatives. As with any exercise, the two most important components are high-quality form and progression.
Progression can take a variety of forms (e.g. more weight, sets, or reps, decreased rest period, improved rep quality, etc) but strive to improve every training session.
Incline Dumbbell Curls Form TipsUse a Reasonable Bench Angle - Those with preexisting shoulder injuries or major mobility issues should use a more upright bench angle of 60 degrees rather than the traditional 45-degree angle used for incline bench exercise. Doing so will remove some of the stress from the shoulder and rotator cuff muscles while also ensuring the biceps benefit from the stimulus of a curl movement at an incline angle.
Minimize Elbow Flaring - In addition to using conservative working weights on this exercise ensure your upper arm and elbows stay vertically in-line with each other throughout the entire movement. If you find yourself flaring your elbows and upper arms to complete the movement then the weight is too heavy.
Keeping your elbows in-line with your shoulders will maximize bicep stimulation.
Avoid Momentum - Perform the incline dumbbell curl in a controlled full-range of motion. Check your ego at the door and don't immediately attempt 75lb dumbbells. Stay tight throughout the movement (abdominals and upper back squeezed) and don't allow your shoulder to roll-in or move up towards your ears.
Do not use momentum to swing the dumbbell from the bottom to the top position. This momentum dramatically increases the likelihood of injury and minimizes the stimulus of the target muscles.
Hold the Squeeze - Increase intensity by holding the top position of the incline dumbbell curl for 5 to 10 seconds. Really focus on squeezing the biceps and gripping the dumbbell as tightly as possible.
This will increase time under tension and the burn in the brachioradialis and biceps. Increased time under tension is an excellent variable to adjust for progressive overload and enhanced muscle growth.
References1) Griffing, James, et al. "Dumbbell Incline Curl." ExRx.net. N.p., 2015. Web.
2) Griffing, James, et al. "Kinesiology Glossary." ExRx.net. N.p., 2015. Web.