Here's the thing. When you read these boards you may well feel like "most people" will get to book before you. But in fact, most people are first time cruisers like yourself, and most of them don't even know about the 75-day window, let alone that they can log on at midnight on that day when their window opens. So actually, most people will be booking things after you.
Having said that, if there are events or times that you are particularly set on, do log on ASAP and grab them. But don't worry, even if you don't get things, there will be cancellations later (check back online regularly) and a lot of things can be signed up for on the ship too.
Two more tips that I give:
1) If you have a large group (or even a medium group) and it says something is "unavailable" for your number of people. Try putting in a lower number or even 1. Grab all the spots you can and get the rest later as people cancel.
2) If an early PAT is really important to you, when filling out your online application, go through it first with answers that won't require additional info. (Say you are driving, using a Driver's Licence for ID instead o password, paying by cash instead of credit card etc.) That will allow you to get through the check in process fastest and select a PAT. Then you can go back and edit your answers to provide Flight info, Passport #s, Credit Card info, etc. after you have your PAT.
Have fun!