here are tips which might help you: -
diet: -
take high protein like milk, eggs, soya and eat fish
exercises: -
breast massage with olive oil in circular motion
jogging, yoga (breathing exercises) can help u in that
even while u walk, walk in firm pose
more than push-ups inclined bench press, declined dumbell flies and pecdec can be more helpful, use light weights and 12-15-20 reps only and dont do everyday, alternate with yoga. jogging