Most card games have a fairly common etiquette. One rule for Rummy I know of is that you should announce any intention to adjust the visible cards before touching them, to indicate you are not taking one.
What are the other common rules of etiquette for Rummy?
Most of the etiquette for Rummy is built into the rules. For example, it is etiquette to "call" a Joker as both a card and a suit the instant it is placed on the table within a combo. That said, tournament rules do add a bit of game play to them that you often find implemented in various groups to some extent. I've also been at a new table (mostly with relatives it seems) before and been surprised to see play accepted that is widely considered "coffee-housing."
My favorite on-line help page to point new players at is: Rummy Talk.
