Time to join a precision rifle forum. They talk about this all the time.
Good glass matters. Save up, as discount brands won't work so well, especially at dawn and dusk, but you may also see distortion, increased parallax, and chromatic aberation.
Biggest tube you can get. Now this isn't quite universal, but I tend to say a 34mm tube if you can get it. More light goes through it. But see below on size and weight as well. 1" is pretty old fashioned now. I tend to say 30mm is a minimum now.
Mildot, and practice how to use it. Some other ranging reticles work, but hard to pick one as they are all proprietary.
FFP so it works at all magnifications.
Side parallax. Understand it.
Understand eye boxes. How much can you move your eye around and see, at all magnifications. It gets narrow at high mag.
Target turrets (exposed, so you just dial in). With MIL/MRAD clicks.
Zero stop. Man did that stop a lot of sign errors for me!
100 m/yd (depending on your system) zero.
Figure out max range needed, and get the least scope you can for that. How much? Depends on—as mentioned above—need for PID. I think 1x / 100m is a bit low, and run more like 2x that mag typically (e.g. 6x at 300 yds) but that's for quick shots on the range. To find stuff, pick aiming points, to ID what I am looking at, I run more. I have a 4-16x and use fully 16x mostly for c. 1000yd shots, but sometimes to see what I can see. I tend to say: borrow some stuff and try it in typical conditions in your local work environment if you can.
Figure out max range needed (and expected of the system) and could total clicks, then run dope to see how far that gets you. Tilted bases give you more room to dial in longer ranges. But, you may not need it so don't default to it.
Range card, ON THE GUN. Once you know distance, be able to dial in rapidly to hit at that range.
LRF. It is hard to estimate range. You probably need a wide FOV scope anyway, so get a small monocular or binocular rangefinder and keep it around. While finding targets, or surveying the scene, you can get the ranges.
A notebook. To make a range card, but also to keep track of data as you shoot generally, develop loads or techniques, etc. A log book, optionally.
A Kestrel. Wind matters, especially as range climbs and with small bullets.
Software on the phone or a ballistic computer. I use Strelok, others will do. Some Kestrels (mine, though I do not use these features because: mobile phone app) also have ballistic computers.
Clip on. Now I know we're getting well outside the scope of what scope, but worth thinking about. If you need day/night capability, think about the fact you may want to stick a clip on NV (maybe thermal) in front sometime. Do you have the rail space with the rifle configuration? Mine was, as it turns out, a bit marginal because my scope is awful big. If I had planned ahead better, I wouldn't have gotten such a big scope.
Similar: Size and weight? If you are going to hump this, or hold it all day, or sneak into places with it, think about that as well. There's a lot of range in size and weight of these.