After carrying your precious bundle of joy for nine months, you've given birth--and now the hard work begins. In addition to caring for your baby, losing weight and regaining your pre-baby figure likely are high on your to-do list. You may have a difficult time achieving a flat stomach after pregnancy because your muscles have weakened and moved to make room for your baby.Plan a healthy diet, exercise consistently and use resistance training to tone your muscles to lose the baby weight and get a flat tummy.Step 1Eat a diet filled with nutrient-rich foods, such as fruits, vegetables, low-fat dairy products, whole grains and lean proteins, recommends MayoClinic.com. Such foods will give you the energy you need to care for your baby and exercise--they also will make you feel full, yet help you lose weight.Step 2Practice proper posture, which may have suffered during your pregnancy. Slumping shoulders and poor back positioning can make your stomach appear pooched. Improve your postural muscles with exercises that strengthen your back and core muscles. Yoga and Pilates are good choices because they focus on making slow, controlled movements while strengthening your muscles and emphasizing good posture.Step 3Perform exercises that strengthen your abdominal muscles. Get clearance from your physician before training your abs, particularly if you had a cesarean section, which can injure your muscles and require time to heal.When you're able, performing an abdominal crunch can help. Lie on your back with your feet on the floor and your fingers laced behind your head. Engage your abdominal muscles to lift your head and shoulder blades off the floor. Perform three sets of 10 repetitions. Gradually work your way up to 30 repetitions, recommends "Good Housekeeping."Step 4Engage in cardiovascular exercise, which helps you burn calories and lose fat from your belly. Examples of good exercises include walking, swimming or riding a stationary bike, according to MayoClinic.com.These exercises get your heart pumping, yet minimize the damage to your joints. Incorporate your new baby into your exercise routine. Buy a jogging stroller and take your baby with you when you walk.