For travel with the USA (this includes going to Alaska and Hawaii) you should arrive at the airport at least two hours before your scheduled departure time.

For international travel (including Puerto Rico, even though it is a US territory) you should arrive at the airport at least three hours before your scheduled departure time.

Those are recommendations all travelers should abide to, whether they travel out of an airport with only three or four scheduled flights a day or a hub like EWR. During the holidays and any other busier travel time (like now) I would add at least another hour on top of that.

This part will generate controversy... make sure when you arrive two or three hours before your scheduled departure time that we are talking about the moment you walk into the terminal, not the moment you drive up onto airport property and then spend 5-10 minutes looking for a place to park (and then there's also the shuttle to the terminal, if needed). You need to give yourself enough time if you need to check any bags, go through security, etc.