From a strict interpretation of the elite rules, CL floor upgrades is not a benefit for a Silver elite. With that said, a given hotel may depending on various issues like how full they are, the total number of elites, number of empty CL floor rooms, their own internal rules for upgrades, etc, may give a Silver elite upgrades from time to time. (Its possible that the CL floor was fairly empty, but rooms on other floors were more utilized. Therefore you may have received what some on the airline forums refer to as an "operational upgrade". They needed your room for someone else. They could have decided to upgrade a Silver elite rather an a non-elite.)

There are actually a number of reasons you may have received an upgrade. The moral of the story is that in general, as a Silver elite, you probably won't see a lot of CL floor upgrades. Enjoy it when it happens.

As for tips, you can always ask about a possible upgrade when you check in. You may get lucky once in a while. You can also contact the local hotel management a few days before you arrive to let them know you are coming. Let them know you are looking forward to your stay there and would appreciate any upgrade they might be able to throw your way. I would also tell them that you understand that the upgrade isn't guaranteed or required, just appreciated if it happens.