Planning is half the fun of a trip! Sometimes you almost need to start at the end of your trip & work backwards particularly if flights back to your home city from your last stopover point are not on a daily basis.
Seating. One of the thing you need to do early once you have your flight bookings are pre-allocate your seats. This would be automatic for most here on AFF but a lot of people don't do this and leave it until they arrive at the airport. We were on a YASA SYD/DFW last year but snagged 69JK which is a pair of two seats towards the back of the 744. Eliminating the 3rd person who either has to climb over you (or you them) definitely makes life easier.
Phones. When going to the US we have a phone we use only over plus a US sim card with a permanent cell phone number so we're not mucking around taking sim cards out of our regular phones. Most companies ask for cell phone numbers at the time of booking eg airlines/shuttle bus/day tours. It's a real time saver not having to waste time sorting out comms on arrival so you can hit the ground running.
Sometimes at US airports you can't find a public phone when you need one and there are zero public phones at other places like the Grapevine Mall at DFW so we had to give a store employee some money to use their phone to call our hotel shuttle to come and get us.
Ground transportation/shuttles. How are you getting from airport to hotel? I have pre-booked the Super Shuttle in the US before we left Australia by using a Global Gossip calling card & ringing 0011 1 800 Blue Van. You can pre-pay the whole thing - fare/taxes/tips etc but take a print out of the confirmation so the driver knows you've paid. Again already having your cell phone is invaluable when you're arriving at JFK at 2200 on a Sunday night to liaise with the shuttle bus company where to meet up.
Lounge access is another this to research beforehand which may depend on what gate you're next flight is departing from. You sometimes have to weigh up whether to use the OW or *A lounge vs the Priority Pass Lounge. Do you have to pay for the guest & if so is it worth it for whatever they have on offer food & drinks wise.
Top of my list would probably be which lounge offers the best view of the active runway and or aircraft as having no view sucks and I would rather be out in the terminal. If you've got kids in tow you'd want the lounge with the more generous guest allowance.
Travel apps. I find Tripit invaluable as in the planning stage you can synchronise your Gmail with Tripit and send any travel related confirmations eg airline eticket itinerary receipts, hotel confirmations etc to that email which will automatically download into Tripit as previously you had to forward the confirmation email to
[email protected]. You would be amazed how many times you'll refer to it for things like airline pnrs when checking in online or at an airport kiosk, hotel phone number, double checking what time your flight departs the next day etc.
One good thing about this app is you don't have to have wi-fi access to refer to access your itinerary so you can have your phone in flight mode or if you're in a taxi & need to check the hotel address it's at your finger tips.