Something really important to think about is the position of the light source in relation to the lens. If you have c it too close to the lens you can get a thing called backscatter. Here is the dictionary definition of backscatter.
So in other words, backscatter is an underwater version of cats eyes. Muck and dead skin is lit up by the light from the strobe. If the lights are pointing straight forward they are more likely to bounce light back inside the lens and show up add ghost spots. One way to avoid this is the angle your lights forward but slightly off to one side. I will add an example slide to the next post.
Tim Los Photographer Leeds York 