Electronics are cool and great to aid in LRS, but get use to manual ranging. Use your reticle, learn it. I think its fun to go out and just do the math in my head and range. Usually I'll bring out my range finder and double check my math. I've been estimating the height of an object close to the area of my target(a tree, stump, downed tree, width of a logging road), ranging from that guess. Then, the electronic rangefinder comes into play. See how close I actually was.
Good luck with that. I have ranged deer successfully out to 880 yards (within 8 yards) and I have misranged deer at 390 yards (was almost 100 yards off), if you can guess the size of a tree you are better than anyone I have ever seen. I don't feel comfortable past 300 yards knowing I'm going to hit a small target. I've cleaned UKD courses before but target size and distance has really helped me out. When you in the ELR game, time to bust out the tools. Don't get me wrong, I try my hand at it too, but I try the lottery and feel better about getting that one right.
OP, Wind reading skills. And a really good LRF. You need to know the range before you can put an educated hold on it. Oh, and good software, oh, and good rifle, oh, and good scope, oh, and good load.
Wait, that's a lot of stuff. You cant get by cheap. Want good results? Get good gear, and all of it. Everything is important. Give me a 408CT and no form of ranging targets you might as well give me a 308.