Your post asks about " rooms you are entitled to" as a person with status - in those circumstances, I have found the process to be fairly automated, esp as a Plat. If that is truly your question, no action needed, just show up. I rarely have problems.

The other responses are for gaining upgrades above and beyond what you're entitled to or have booked. In that case, any / all of the methods outlined can work. Asking nicely and making it clear you realize it is an " extra " is most important IMO. I would add one thing - I always call after receiving the upgrade (or whatever) and thank the person involved. Truly above and beyond merits a letter to Marriott CS.

I am in the DJ_iceman camp - on my own, I do not care, but for family / special occasions I tend to request. And Kudos to Marriott, they have never let me down. ^