Resistance, placement and control are vital elements that must be addressed in all jazz and contemporary classes. These elements will help them not only to progress, but to reduce the chance of injury.
Resistance: Arms must have energy to them at all times. Have the students place their arms in Jazz 1st and long 2nd, and gently press the arms down, while they try to maintain their position, this will help them to understand the feeling of energy they must have as opposed to tension. To help them understand tension I will have them lift the shoulders with arms in 1st position then press them down. Repeat this several times so that the feel the difference. The same must be emphasized in the legs when feet are in the Jazz or Ballet 2nd, in these positions the knees have a tendency to cave in. You can help them avoid this by having them stand in jazz 2nd with their knees slightly bent, apply gentle pressure inwards with both hands, as they maintain their position, to help them understand how this applies. Then by adding a small jump they can see if when they land that the knees and toes are in alignment. Once they feel how to keep this alignment they will understand how to apply resistance in the legs.
Placement: Resistance is the key to proper placement. Once the students understand how to maintain a position, placement can then be emphasized. Placement of the arms, torso and feet should be focused on in every class. This will help minimize rolling in of the ankles and knees. Stress pelvis pressing forward and abdominals pushing in to prevent releasing of the hips and swaying of the back. This is critical for the students. Constant releasing of the hips and swaying the back will not only hamper their balance but increase the chance of back injury. Arm positions should be reinforced consistently. A good exercise is to have them do a preparation for pirouettes in a lunge position. As they reach pass arms go into 1st position. You can go up behind them and firmly press down on the arms out by the elbow. This will help them maintain the proper placement when you add a turn. I will even do this in my advanced classes to reinforce these important principles.
Control: This is the final ingredient taught and is a byproduct of the first two. Resistance and placement help the students find the way to control all turns, kicks, leaps and jumps. Control takes some time to learn because they need to develop the strength first. I like to focus on the lower back and abdominals. Slow movements having them work on these areas will be necessary to build strength. The more flexibility that the students have the more important this will become. This is also very important for the injury prevention. When a technique is executed without control they will release the back and not use the abdominals on the landing of leaps and jumps. This puts a strain on the knees, hips, ankles and back.
Students are always eager to learn more advanced technique, usually before they are ready! Make sure they have proper resistance, placement and control consistently before you teach new material. Once the students understand how the exercises work then they can be taught how to apply these principles to their dancing. As we know, all students are different and the speed in which you teach will vary from class to class. My only advice would be to go slower rather than faster. A clean foundation is best and in my experience produces the best dancers.