Musclechemistry Board Certified Member

First, we want to make sure you train the triceps with full range of motion. The main function of your triceps is elbow extension. So let's train this movement pattern effectively by properly stretching and contracting your triceps on exercises like straight-bar pushdowns. This also applies to rope pushdowns.
Next, we want to prevent losing tension on the triceps whenever you train your triceps with dumbbells. Let's take triceps kickbacks as another example, if you bring your lower arm all the way up to your chest, there is no resistance on the tricep. Instead, try something like a triceps standing cable kickback in which there is more resistance on your triceps.
Also, it's beneficial to train your triceps from different angles. Since the long head of your triceps attaches to the shoulder, you are able to train the long head at different muscle lengths based on your arm position. I suggest including a triceps exercise in which your arms are at your side, overhead and at a 90-degree angle (this can also be a horizontal press).
Lastly, the triceps aren't just trained with isolation movements, but also with compound movements like the bench press and shoulder press. If you want to focus more on your triceps in your training, try progressively overloading exercises like dips or the close-grip bench press.