Unless you are trying out for the announcing position, just ball or strike will do.
Some teach subtle motions of the head (up, down, left, right) to provide the pitcher an indication of where you saw the pitch. As long as they remain subtle, I see no problem doing that.
Some teach a very short and quiet comment to the catcher, but there are coaches, especially in the NCAA who do not want the umpire to talk to the catchers at all.
What the umpire shouldn't do is provide an exaggerated movement, point or announce the location of the pitch. The umpire shouldn't be part of the show.