To master idioms, start with those most frequently used, like "A piece of cake" for something easy. Practice them in sentences to get comfortable with their context. Read extensively, paying attention to idioms in books or articles. Keep an idiom journal where you jot down new ones, their meanings, and example sentences. Engage in conversations with native speakers, and don't hesitate to ask for explanations when you hear a new idiom. Over time, using idioms will become as natural as speaking itself, boosting your fluency and confidence in any conversation.