Even though veneers can do amazing things, I would not consider them on severely crowded teeth before having a consultation with an Orthodontist. You want to make a decision knowing all your alternatives. Like Dr. Jablow said, if you get your crowding corrected before you do the veneers, the tooth structure to be removed is going to be much less and the gum health much more improved. You could also avoid the veneers all together if the shape and color of your teeth are fine. On the other hand, if having braces or Invisalign is not posible, veneers can do the trick under the hand of an experienced Dentist. Just make sure you know exactly what you are getting into and make a decision knowing all the alternatives.