Be sure to empty the saucer after it drains so the plants won't sit in water. They are probably more tolerant of dry air indoors than many other plants, but they prefer not to be near heat vents or cold air returns. Mums will flower well without any additional fertilizer if they are purchased already in bud. If they aren't blooming yet, feed them every other week with a water-soluble fertilizer such as Bachman's Excel Gro. Chrysanthemums prefer a quality potting soil such as Bachman's Exceloam or a soil-less mix such as Hyde Park Professional Mix.
Good drainage is important.
Because they don't make good garden mums and they are very difficult to rebloom, there is no need to repot them. Just discard the old plant and replace it with a new one whose buds are just beginning to open. Chrysanthemums are not hard to keep looking great. All you need to do is remove spent blooms as soon as they fade so they won't detract from the other flowers and buds that are just beginning to open. If the leaves begin to get a little dusty, just give the plant a gentle shower.