Same really good tips up here.
I'll throw in a few more.
First, i'll reiterate the vermiculite. That is not easy and not easy to make it look right.
Don't take the flex pvc that comes with the kit, use 2" rigid.
Don't order the liner with the kit. Once you have the pool in and ready, measure for the liner and get a perfect fit. Took my wife and I maybe an hour to measure and it is custom, fits like a glove. Yes you have the dig sheet but the dig can be off.
When putting in the liner, bite the bullet and buy cyclone liner vac. This machine makes the liner job much easier, costs a little over $300 but then you can use it for winterizing year after year. I used 1 on my 18x36 and the line was stuck tight to the wall withing minutes and this thing ran a looooooong time as I filled from my well.
Get a massive tarp. If you are like me it will take a while to complete. Mine took 4 months total, started in March and filled it July 1. I used the tarp to cover, let it fall down in basically like a liner. Rain would pool in it, then when I was read to work I would throw the pump down in and pump it out and pull the tarp back to a nice work area (ie not mud).
When calculating vermiculite, order more than you need. It is cheap enough, inexperience will dictate you will use more than a pro. We ran out and I had a 7x7 area that had to wait 1 week to get finished until I got more.
Rent a tranist! This device will make life much, much easier. You use it to check the height of all the wall to make sure they are consistent. You then use it to check the depth of the pool floor in various place to make sure it too is level and accurate. Might even try to buy one used and then sell it when done. I was fortunate in I had family who had one.
Buy lots and lots of string line!
Measure, measure, measure. I am overly detailed but I measured and tweaked a ton to make sure the pool was square and square to the house.
Buy a wetsuit! lol .. for me, my well water was a brisk 55 degrees. To cut in the light in the deep end I had plans to go out on a blow up raft and cut it in. That went horribly wrong, so I bit the bullet and went in walking the edge so mainly just legs in the water. It was painful! The alternative was to hang over the edge and do the work, this seemed like a bad idea to me hanging over with a razor cutting the liner. I could see me dropping it in the deep end!