There is no one way to do them. As long as it is controlled you can go fast, slow, or use a tempo. You can choose not to lock out at the top of the movement to keep tension on your arms and chest to make them a bit harder.

I concur.

I have done all sorts of dips and they are all effective.

Lean forward to recruit your chest.
Lean back(straight up) to recruit more triceps.
Add a dip belt.
Slow negatives (5 sec)
Hold the top, focusing on the isometric portion.

In fact, I read a thread on here a few months back on how a dip can give you a helluva chest workout. So I added weight, leaned forward and holy shit. I felt like I was benching all dy.