Think of it as three Harry Potter rides...Forbidden Journey, Escape From Gringotts and Hogwart's Express...none of which take Express Passes, so they don't do you any good for Harry Potter...or do they? They allow you to ride most things without much of a wait, if any, which allows you the freedom to ride the Harry Potter stuff when you can, without worrying you will miss out.
So, best way to make sure you ride those? You will get various answers, so I will start off with my suggestions.
Get the Universal Orlando App for your phone...it will tell you what the wait times are and you can decide when you want to hit them.
Best chance to knock out FB is to do the early admission and when you finish FB, head over to board the Hogwarts Express...then try to hit Gringotts.
As an option, you can also take advantage of the Single Rider line, when they have it open at FB and Gringotts (not available on the Express)...however, you will skip quite a bit of the 'Experience', so I recommend this option after you have gone through the main queue at least once.