Step 1: Find a Good NY Pizza Place
I almost always order just a plain cheese pie - this is New York PIzza in its purist form. No need for toppings, I think it's plenty good just like this.
I have included just a few pictures of the pizza making process below. I think that just some of the key factors into making great New York slices are:
-good sauce to cheese ratio
-proper high temperature oven (see large pizza ovens in background of photos)
-the right type of cheese - you want a little bit of the orange oil that accumulates on top once it's done cooking
-cooking the pie directly on the oven surface - whats the deal with pizza shops using those wire grates?
There are many many more factors that go into making a great slice - but I am not qualified to deal with them all, I just have my own personal preferences.
Check out Jeff Verasano's NY Pizza Recipe for the most complete guide on New York Pizza I have ever seen. (Thanks Jeffreyf for the link).