Navel piercings are very popular but they heal slowly. Healing time is usually 4-9 months, so you have to be patient.
Shower the piercing twice a day with warm water to get interstitial fluids and other impurity out. Do not use antiseptic liquids, they dry the skin and may cause the piercing jewelry to grow out.
Do not go swimming, especially in swimming halls, for 2-3 months. For a first week you should avoid heavy exercise as well. Wait at least 4 months until you change the first piercing jewelry, if you do it too early it may irritate the piercing and healing time gets longer.
Avoid tight belts and trousers/skirts that may irritate the new piercing. For a navel piercing the best shape of jewelry is banana. Ring moves a lot more and brings unwanted bacteria to the wound. That's why we always use titanium or bioflex-banana.