Fundamentals are the same at 100 yards, and 1000.
Trigger control. Respiratory control. Consistent cheek weld and sight picture.
Consistency. Did I say consistency?
First time I went from 200M (the longest available at the local range) and made the long drive to shoot long range (565/1000) I was apprehensive. No need to be..
The only thing that's not easily accounted for- and it is a really BIG "thing"- is the wind. While the effect of wind at 100 yards is barely noticeable, this is not so at 200 and beyond.
Being able to accurately dope the wind over the entire distance of the bullet flight is THE key to being able to hit the target at long range. It can be fairly straightforward on rare occasions when it is consistent or of little value- but most often very challenging when gusting at different velocities, at different distances off the ground, at varying points along the flight to the target. An experienced shooter that's expert at doping the wind will outshoot someone less capable with that skill every time with a rifle that's far less "accurate".
It can be very frustrating shooting long range on a windy day when one has little or no experience. While the only way to get the experience is trigger time, no point blowing $100 bucks in ammo if you lack the skills to make it happen. Gain your experience gradually, picking increasingly difficult (windy) days to hone your skills. Here's a good article on wind...
Elevation is easily adjusted by means of free ballistic calculators online. JBM, Hornady and others are easily used- but you need to know your muzzle velocity, and that requires a chrono for most precision. However, you can "back into" an estimation- when you determine the number of minutes of "up" elevation from your zero range to your long range target, you can extrapolate the muzzle velocity and get it fairly close.
If you have a smartphone, download Strelok- it's a free ballistics program and makes it easy to have the information at your fingertips at the range.