Keep your back straight and don't ever leaning into the chair.
Put both hand on your lap.
Keeping the knees together and your leg at slightly more than ninety degrees will make posture appear gracefully.
Know how to handling something
When you handling something, in this case is the cup of tea, avoid making distraction noise. You can put your pinkie on the saucer (if there's saucer) or the table.
Pick up or lower the cup slowly.
Know how to adding sugar on her cup
To add the sugar on your tea o coffee, put the sugar on your teaspoon and slowly lower it to your drink.
Don't forget to remove the spoon and place it to the side.
Now you know how to act like a lady at the formal party :)
Live to Love
Baby, S. 2008. How to look like a lady. Gothic and Lolita Bible