Things that have helped me secure pre-orders in the past, including managing to get an original Apple Watch on launch day:
Get up 10 minutes before pre-orders start and get your computer/iphone/ipad/whatever all ready to go. If you are worried about something going wrong get up earlier or don't even go to sleep!

. This is absolutely vital, if you aren't awake the second pre-orders go live you won't be getting this thing at launch.
Seriously watch this forum LIKE A HAWK, I would say hitting F5 here is as important as hitting F5 on the Apple or carrier site. The reason is that, and this has happened to me I'd say 80% of the time with pre-orders, the website for doing the preorder will go up but won't display on the main page for most people so there is no way to access it. Usually someone on here will find it somehow and post a link or instructions on how to get it. For example last year I managed to get a 7 because someone in the Verizon thread said you can use their app and use their automated assistant thing to order it, this happened like 5 minutes before the official pre-order start time.
Use all the devices you can. Sometimes the apple website gets updated first, sometimes the apple app, sometimes the carrier website, etc... Also force closing the app and then reopening it helps as well as does searching manually for the product. I got the Apple Watch on launch day, even though that sold out within minutes too, thanks to the app on my iPad opening up orders before the website or the app on my phone.
Have all your payment info ready to go asap! Don't keep this around but you could even do something like type it all out in a txt document for a quick copy and paste. Double and triple check your number and exp date! Keep in mind that with Verizon at least they require your payment card to have the same address as your account billing address! The account is under my wife's name so I usually have to use her card to be sure...even though you will probably pay $0 upfront they still need to verify the stupid card! I dunno how the other carriers work and this isn't the case ordering directly from Apple. Oh and with the Apple Store apps they support Apple Pay so make sure your card is all set to go there for even faster checkout.
Finally even when the dates start to slip don't lose hope and go ahead and place the order anyways! Apple is typically fairly conservative when estimating things and this carries over to ship dates. From my experience actual ship dates tend to be about a week earlier than estimated when they go past the launch date. Who knows if that will still be the case here with supply as short as people say but I believe this even held true with the original Apple Watch which was also REALLY supply constrained.
Hope this helps someone!!! Although hopefully not too many people as I don't want too much more competition for my pre-order!