Moisture in your ears is most commonly caused by spending too much time in the water such as in a swimming pool when you have your head under the water.
Sometimes moisture gets trapped in the ear and you need to get rid of the swimmers ear by draining out the water.
Other times the moisture in your ear can be caused by humidity in the air or if it's raining a lot then sometimes moisture can get trapped in your ear.
Condensation from the air is another way that moisture can be trapped in your ear as well.
You can use a hair dryer to help dry the moisture out of your ear and use some rubbing alcohol to clean your ears since the rubbing alcohol helps to absorb the moisture so that it evaporates.
If you have chronic moisture in your ear then you should use rubbing alcohol daily and see your doctor about it to make sure it's not caused by some medical ear condition which can usually be treated.