Dips
Have the body in a straight up and down position (180 degrees). The body will tend to lean a bit forward when dipping, calling on the delts and pecs to assist. If targeting the triceps, you do not want that. May have to have a training partner help steady and hold that 180 degree position for you. Or prop the feet/lower body against something; bench, chair, etc.
Would suggest a "V" bar for dipping. With focus on the tricep you want a closer to the body, elbows in position for the complete rep. Flairing the elbows out during the rep takes away the full affect of the exercise on those triceps, calling more on the delts and pecs for aid. If not having a "V" bar, than any device that would help with a closer dipping hand position.
Going to fine also that you will not be as strong in that true straight up position dip than your are in the regular dip at first. It can be an ego buster for some. But well worth the effort for tricep mass.
Good Luck