How do you read the wind? Please explain.

I'm sure you're an awesome shot and all. Curious to how many animals you've missed at 600+.

I have a friend or two that know a little about taking a long shot. One's got a nice .284 with a quality scope and vector rangefinder. I've seen him twice take animals past 700m this year. My 13 yr old son rolled behind his rifle and his a volleyball sized rock at 1380m, first shot. But that was after he'd dialed the wind tightly with two shots.

So my question is, how do you "read the wind" with confidence, at 1000? Just curious.