Whichever is the most popular ride that we want to do, we'll head to first. I think the key for any theme park is to get there for opening (as in be parked up, tickets purchased and at the turnstiles/rope drop before the park is due to open) From there we'll usually do any other popular ones in that area, then head to the next area with popular rides. However, if there are Fastpasses (like at Disney parks) we might get one before doing our first ride of the day if they are available.
As an example: At Alton Towers a couple of weeks ago we headed to Rita Queen of Speed first.. (since it's the newest and seems to be the number one ride right now) The opening time was actually 10am but they let people in to park from something like 9 and the queue was already at around 15 minutes by 10am when the ride opened. From there we went straight to Nemesis and Air and had done the three most popular rides way before 11 when the crowds were pouring in!