Mr. Ed,
Sewwhat89 has pretty much overed things very well so I will simply review what he has already stated.
1. Equipment.
It is imperative that you have gear that you know is top quality. You can not learn long or extreme range shooting skills unless you know the equipment you are using is fully up to the challange.
The reason is that if you have a rifle system that is up to the challange and you make a poor shot, you know that you are the weak link in the system and you can learn from that miss and do better to prevent the same thing on the next shot.
If you do not have quality equipment, you will be wondering it the problem is the rifle, the load or you. Nothing will come from that, espeically confidence.
2. I agree on the practice issue, it is second only to the equipment in importance. This is a year round thing, even if in limited ammounts, you need to shoot year round to stay proficent at longer ranges.
Also, practice at the ranges you will hunt or better yet even farther. If you practice at 500 yards all summer, when the buck shows up at 400 yards you will be ready to take and make the shot.
Practice at varying ranges. Get your rifle/load system set up and ready to roll and then practice at varying ranges, do not set a target up at 200,300 and 500 yards and shoot only on paper at these ranges.
Set water filled gallon milk jugs up at varying ranges, range them, look them up on your drop chart and target them. If you hit record the hit that your drop chart is on at that range. If you miss, record the miss and by how much. Doing this over many ranges will allow you to tweak your drop chart until you can run the table from the muzzle out to however far you want with an accurate drop chart and rifle/load system.
3. Confidence and even more importantly humility is key in long range hunting. It is vastly more important to know when NOT to shot then anything else. Remember that a wounded animal at long range is much more difficult to correct then a wounded animal at close range.
Neither is acceptible but it is critical at long range that we know what we can and can not do. This will vary with field conditions.
I will admit that in good conditions I would take 800 yard shots on big game. If the wind picks up to 10 mph or so I will drop this range to 500 yards at the most. In heavier winds, I will limit my shooting to 300 yards at most. This is what you need to learn and again, it only comes from practice.
To that point, do not only practice when its nice out. Some of your most valuable range time will be in windy conditions. Unless your zeroing a scope or testing the accuracy of a load, get out there and shoot when its windy!!
Kirby Allen(50)