It will benefit everybody if you know the basics of gambling protocol before you sit down for the first time. Few things are more annoying than a beginner at a table who doesn't know what to do and has to be told everything several times by the dealer. Before your first time at a table game ask if your casino offers gaming instructions. Many will give a tour of all the major games, explaining the rules and how to play, at specific times of the day.
Some casinos offer a designated table where people can play with play chips to get their feet wet.
If none of these options are available I would suggest watching a game from behind for a few minutes before sitting down. Notice the procedure and when you sit down try not to disrupt it. Only buy or cash in chips between hands. If you sit down while a hand is in progress then wait patiently for the conclusion of the hand to buy in. Use this time to get your money ready.