I've harvested a couple diamonds whose score was at 950 or barely over to the point where if I'd lost even 1% of the quick kill bonus they would only have been Golds.

Be sure your conseq kill rate is at 100%, don't use a more powerful weapon than what is recommended for the species and practice those spine, heart and/or brain shots. The max levels of the various species and the TR and weight ranges can be found in the Tips and Tricks section of this thread. Most of the animals you harvest will be on the lower end of that spread as opposed to the higher number so the higher that lower number is the better. The weight ranges shown in tracks can be helpful in identifiying potential diamond quality animals.

Your binos have x-ray vision, just be careful because you might hit the hill or tree or rock that the binos illuminated the animal through. Best thing is to what you've been doing except to look around before you pull the trigger. Mostly it's blind luck as they don't vocal much and depending upoon the species, diamonds can be loners.