2 questionswind matters most at the shooter's location. start with that, and then try to spot some vegetation/tree leaves 1/3 and 2/3 to the target. no value winds are the hardest because a 10-15deg shift in direction can put your holds on opposite sides of the target. much easier to bracket your wind hold with a full or half value wind.
Have you ever seen someone hang a short piece of yarn from the muzzle end of the barrel to get an idea of wind direction and velocity? I've seen this, but not sure of it's effectiveness.
What magnification do you like to set your scope at when shooting at 300 yards and out? Too much magnification makes it difficult to keep it on target to spot your misses from my experience.