Great question
@montyhiker. In Galicia, I usually sit down and wait for a server to come take my order. At times I've gone to the bar and ordered something, but I honestly can't remember the last time I took my own plates/cups to a table - usually the bartender would take the order at the bar, and then bring it to me at a table.
And - just a note that in some bars and restaurants, they don't want you to clear your own plates/cups. They'd rather do it themselves, and it would disrupt their system if you were to bring your plates and cups back to the bar once you were done. Perhaps look around at what other patrons at the cafe are doing and follow suit.
Also, during busy periods, if you do want to be seated, there is sometimes a queue of people, but you don't know it! Often Spaniards will check in with a server, be told it's busy and to wait in line, and then they'll mill around/ sit on a wall nearby or across the street/ sit at the bar. The server will know in which order everyone came, and he/she will direct you once it's your turn to be seated at a table. If you do try to sit down at a table before it's your turn (or without realizing at all that there was a queue!), someone will clearly tell you that it's not for you
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Buen Camino!