Dips can be tricky. We need to create and external rotational force withe shoulders in extension. The elbow should flex to the range in which the shoulder can keep external rotation. To go all the way down with a few plates as shown here is tough. I do not recommend using heavier weight until you have mastered technique. With weight, go slow eccentrically (down) so that faults in the chain can be easily identified and altered. I love dips as a burnout after a few heavy presses. For bodyweight, try to work up to 4-6 sets of 8-12. When this can be complete, move to the weight belt. My favorite weight belt is still the old school Harbinger belt, mine is 4 years old still strong. For strength, try 3-5 sets at 4-6 reps.