When you know what areas you need to improve, you'll have a sense of direction and you'll no longer feel blind-sided by these mysterious social errors. Look for clues in your environment to help you decipher the subtext. Be mindful of alternative possibilities. Be aware of body language, tone of voice, behavior and the look in someone's eyes to help you interpret what is really being said. Look at the choice of words the person uses to help you detect the subtext.
Actions speak louder than words.
If someone's words say one thing but his actions reveal another, it would be wise to consider that his actions might be revealing his true feelings. Find someone to act as a guide to help you with this hidden language. Compare your understanding of reality with the guide's understanding of reality. If there is a discrepancy, you might want to try the other person's interpretation and see what happens, especially if you usually get it wrong. Learn to interpret polite behavior.