I concur with those who say you should familiarize yourself with the listed benefits, so that you don't expect too much, too little, or the wrong things.
When making online reservations, I always put something in the comment field such as: "Request Gold benefits & upgrade if available. Thanks!"
As I understand it, these comments are usually read by someone on the day you check in (or maybe the day before?), so they possibly help remind them of the status perks you are due.