Some ways to get rid of the mildew smell are to eliminate the source of the smell, clean up the area with bleach and wash fabrics thoroughly. It is also a good idea to keep the humidity low to reduce moisture, which adds to mold and mildew.
To remove a mildew smell, you need to know exactly where it is coming from. Narrow down the smell to the main room it is in, and then sniff around to find the culprit. It is usually near moist or damp areas, so in the bathroom, it might be underneath the sink or on the shower curtain. If it is the shower curtain, either clean it with bleach, or throw it away and replace it. Mildew on bathroom surfaces, such as floors and fixtures, need to be cleaned.
If you can't find exactly where it is coming from, clean the entire area with a bleach and water mixture. This helps to remove mold and mildew and give a fresh scent to the room. Be sure all bleach is rinsed thoroughly. For mildew on fabrics, soak them in bleach that is appropriate for all fabrics, and then wash them like a typical load of laundry. After eliminating the smell, prevent mildew in the future by using a dehumidifier, and keep areas with dry a ceiling fan.