Tip 1. Train the arms at a variety of different angles in relation to the torso- This ensures development of all parts of the biceps and triceps. E.g the Incline Dumbbell Curl will place more focus on the long head of the Biceps Brachii, where as High Pulley Curls will place more focus on the short head of the Biceps Brachii.
Tip 2. Alternate Biceps and Triceps with Super Sets- This means performing a set on the biceps, taking the required rest, then performing a set on the triceps, then repeating for the required amount of sets. This allows a greater amount of work to be performed in a given time period, as you are working the triceps during part of the recovery of the biceps where you would normally be resting. This method has also been shown to stimulate a greater amount of muscle fibres than just training one muscle group alone in a set.
Tip 3. Use a variety of grip positions- The grip that is used on a given exercise changes the extent that the muscle, or part of the muscle is stimulated. E.g a Barbell Preacher Curl which requires the grip to be in a supinated (underhand) position will mainly target the Biceps Brachii, but when the exercise is done with Dumbbells with a neutral (Hammer) grip, the the Brachioradialis of the forearms are heavily called upon.
Tip 4. Focus on increasing the mind to muscle connection when training the arms- This means really getting a feel for the correct muscle contracting and forcing it to contract as hard as possible. Some ways to improve this are, using a slow tempo (contraction speed), holding a hand on or getting a partner to touch the contracting muscle, closing your eyes and visualizing the muscle contracting, warm up with concentration curls, twisting the hand into full supination at the top of Dumbbell Curls.
Tip 5. Do as many of your arm exercises as possible in a seated position- Doing exercises seated makes it easier to maintain form without cheating by swinging or jerking the body, or rising up on the toes, which all generate momentum and lessen the amount that the target muscle is isolated which reduces the amount the muscle is stimulated.