Get on top of the boom. Go way downwind. Sheet in low with the back hand towards your hip. Kick the board around hard with the back foot. Extend the back hand. (That's Matt paraphrasing. Sofy has much more detail to give than this.)
Kevin told me to go more downwind. Sofy told me to sheet in. What they both were after was that you must really stall the sail.
"Get on top of the boom" may suggest bending both elbows the same, which doesn't really sheet in. I discovered it is better to make your back hand touch your chest, or as close as possible. For a long time I wrongly thought I needed to sheet in all the way before popping. It is better to pop heading downwind and then sheet in hard shortly after that - not like a forward, just pull the clew into the wind and keep it there.
When you bear off you immediately start losing speed. Pop before you lose too much of it, but don't forget to be balanced when you take off.
Remain on top of the board. It may seem too obvious to qualify as a tip, but the thought that got me to make the first one was, "Identify the moment that you go from centered to your heels." (A moment like this is never supposed to come, or maybe very, very late, but just thinking, "Stay over the board" was not doing it for me.)
Another way I thought about it is, "Pop up, not back." Kevin has told me that it is even more important to lean really far forward in the Grubby. I believe it.