I'll add my advice for first timers if anyone wants it...in my opinion, one of the best ways to avoid criss-crossing is to make yourself familiar with maps of the parks well in advance of your trip. Understand how the "lands" of the various parks are laid out. We tend to find touring the parks in a circle is more efficient, and that's how we plan our FPs as well.
I will use the MK as my example, because I feel like it's the park that needs the most planning because of size, amount of rides, and general distractions (taking in the scenery, shopping, snacking, etc...). We tend to always start in Tomorrowland at rope drop, and during my past trips, parts of the park on that side have been deserted. We will do Space, Buzz, Dumbo, Goofy, Little Mermaid, sometimes meet and greets, Small World, sometimes a FP (Peter or Dwarfs), and Haunted Mansion all well before lunch time. Crowds really do tend to pick up around 11:00, and we generally start FPs to coincide with our location and try to time the first one (most of the time we do Big Thunder, Splash, and Dwarfs. We'll plan Splash and Thunder back to back, and Dwarfs either first or last. If first, we hit it while we're in the Fantasyland area in the morning, or last, after lunch, so we can ride it and then leave the park for the afternoon) to land somewhere within the 10:30 - 10:45am window. We'll do the next one with a time around 11:30 - 12:30 so we can catch it close to the end, then do the next 12:30 - 1:30 (this is just an example...sometimes we push them back to end around 2:30ish, which lines up close to the beginning of the FoF parade). We'll leave around that time (either just before or just after the parade), go back to swim and relax, then head back out for our dinner reservation if we have one, or go back after grabbing some food at the resort. Our evenings are usually unplanned, sometimes we pick up a fast pass before leaving the park and time it for 7pm-ish. We'll pick some up if we feel like it during the night, but mostly we just go where the wind takes us.
This approach tends to make us feel secure in that we have something planned, but it's timed out in such a way that it's incredibly flexible. I've never felt too tied down this way, and it offers a chance to take in your surroundings, which is one of the most important things to do at Disney World anyway!
Anyway, that's what works for us! To me, that's the beauty of FP+, I don't have to backtrack. It was rough to deal with that when we were at
Disneyland last month, and I had to go back to getting paper fast passes before they ran out for the day, and hoping that they'd be for a time that would work. Because you do have the opportunity to plan FPs so far in advance at WDW(and you don't really *have* to, depending on your rides of choice, you can wait - but I'm not a waiter! Also, for certain rides, it's just a good idea to go ahead and make the FPs as soon as possible. But now that you're not locked in to making all three at once, you can make the hard ones and then add in the others later if you want to, or if you don't have enough time to sit and do everything at once), you also have time to make changes if anything happens before your trip begins. We've also had success changing entire days around the night before. I'm a diehard rope drop junkie (it's a flaw, lol) so I tend to automatically plan things around early mornings to get more things done. However, during our last trip, we really needed a day where we didn't wake up at the crack of dawn. So we changed every single FP time for the next day, and had no problem replacing the ones we had or changing the times to fit our new plan. We're taking a later approach with some of our days this time around, too, even though it's almost a given that we'll be up early anyway.
. You can officially also put us down as attending 
. This has been a bucket list item since our first Disney trip in 2009!
