What steps and products do I need to paint my avocado green tub to white?

You may want to look into this product http://www.superjetco.com/BathBrite.html Paint doesn't last long on fiberglass unless you sand the entire surface with 180 grit paper and apply a marine boat paint.

Are you sure your tub is fiberglas? Avocado was in the early 70's, not a lot of colored fiberglas plumbing fixtures are that time. Could it be cast iron? Totally different steps to refinish those.

What steps and products do I need to paint my avocado green tub to white?
Yes, it is fiberglas

Yes, it is fiberglas
Can you change the color of an old fiberglas tub/shower to white?