Cause, Feedback, and Transfer
Before giving any feedback, you need to understand the major technical components of the movement you're watching. What does an efficient stand-up look like mechanically? What hip and spine position should a person be in when bridging from bottom mount? Without that baseline, you're just reacting to what looks wrong rather than understanding why.
This matters because multiple errors will almost always be visible at once. A sloppy double leg might show poor level change, a wide stance, a dropped head, and a collapsed posture at the finish. The temptation is to call out all of them. Resist it.
If you see five things going wrong, four of them are probably symptoms. Someone who gets flattened out in turtle may display a wide base, slow hip movement, and poor head position, but trace it back, and the real problem might be that they never loaded their toes. Fix the toes, and the rest may self-correct. The better your understanding of movement, the better you can distinguish dysfunction from downstream consequences.
How you communicate it depends on who you're coaching.
Prescriptive feedback is best for new-to-intermediate grapplers. Tell them exactly what you want them to do, not what they're doing wrong, using a clear, positive directive: "Keep your knees and elbow connected." Simple and actionable.
Descriptive feedback works for the experienced, who have a deep understanding and ability to self-correct once an issue is illuminated. Mentioning "you're leaving your near arm exposed every time you shoot" is enough; they will take it from there.
The mistake is applying descriptive feedback to beginners and prescriptive feedback to advanced students.
Finally, and this is the most neglected question in movement training: Does it actually transfer?
You can drill something a thousand times, but if it doesn't show up in live rolling, it hasn't transferred, and that's the only metric that matters.
If not, something in the bridge between drill and application is broken.