In my experience there seems to be meal choice priority for gold/platinum. I don't really know how this manifests itself though. I have never encountered a situation where my choice is not available.
As Flyingscientist mentions, the status is written on the meal choice sheet hanging in the galley. As I do always board as one of the first pax maybe that helps as well. By the time the flight attendants have brought the welcome drink, wet towel etc they come around for the meal choices directly, rather than start at row 1 and make their way back. I guess that if you proactively show that you have been looking at the menu and are ready to give your choices upon boarding, you could be one of the first to order and all options should be available.
On longer flights with multiple full meals, I typically ask the FA to reserve X dish from the second meal, which they always do.
In economy class the FA or CSM always comes to welcome status holders by name upon boarding and asks which meal he/she would like later on and reserve it. I think this is a nice touch.