Few things are more bothersome than a beginner at a table who doesn't know what to do. 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. When you buy in the dealer may ask what denomination of chips you prefer. This shows you are willing to tip and will help establish a good rapport with the dealer quickly.