How do you install a tachometer on a 1991 Cavalier Z24 multiport with electronic injection?

As far as what tachs will work: buy a tach that has what is called an "inductive" pickup. this is a clip that you put around a spark plug wire, it will give your tach the signal it needs from the engine. the rest of the basic instructions, even though they wont be for your exact car, will be in the package with the tach.