Listen to conversations around you, when you are on the bus or in the grocery store.
“Eavesdrop” means to listen to a conversation that you are not included in. Often it is used negatively (“eavesdropping at the door, hoping to hear secrets…”) – but it’s okay to listen to the people behind you on the bus!
Listen for their greetings, filler words, how they answer the phone, and more. You will notice many natural-sounding expressions. Practice planning your own conversations too – ask yourself, how would I answer that question?