Serve and volley requires a good serve that forces your opponent to hit weak returns most of the time. A good flat serve is a great choice, but over a course of a match the opponent might get used to it and start firing back faster returns. Well it's the same with any serve. Best choice is to have a variety of serves placed everywhere and choose your choice of weapon varying by the opponent. (ex: weak backhand returner. Flat/kick/slice serve to backhand side)
Biggest weakness really are good returners...passing and lobs..are pretty obvious. Good returners even will make it harder to finish off points easily.