Get as much magnification as you can afford in a variable scope for long range.
Mirage may prevent you from utilizing all of it sometimes, but better to have it when you can use it. In any case, I wouldn't go less than 16X. Some will argue 10X is enough for 1000 yards. Not for me...
You need to define long-range...whatever it is to you.
You then need to determine what round you'll be shooting, and what the approximate bullet drop will be at that range.
Equip your rifle with a 20 MOA base. This will help in getting enough elevation adjustment from your scope. Verify that your scope WILL have enough elevation adjustment- even with a 20 MOA base- to compensate for your intended range.
Often, this requires a 30mm tube.
I got a great deal on a Weaver scope with 1/8 moa clicks- only to find out that it has a measly 30 MOA of elevation adjustment, and won't reach out much past 600 yards with a .308 match load- even WITH a 20 moa base.
Do your homework to make sure it will work at the maximum range you will be shooting.