There are maaany, many, many threads addressing it in DB - just use the search function. Generally, it is advised getting the ears clean and dry after the dive as soon as possible. Different solutions, including a mix of vinegar, alcohol and hydrogen peroxide, are often proposed. Many divers use a drop of medical linen oil into each ear before the dive. Some divers swear on ventilated diver ear plugs (i.e. PRO plugs). Do not clean or dry your ears mechanically, use just dry warm air. Visit your dentist and have your teeth carefully checked - ear infections are often related to dental problems.
Read more for example here:
http://forums.deeperblue.net/safety/...ghlight=otitis
http://forums.deeperblue.net/safety/...highlight=ears