If you are always outdoors, the sun and rain do a lot of damage to hair, and this causes it to dry out, and hence you may have to clean it more often.
Cleaning your hair daily is a good idea if you have the time, but this means you have to dry it out every day which is not always a good idea.
Try and wash your hair at least twice a week.
Washing your hair with a good quality shampoo will help with getting rid of dandruff and dryness as well. It will also help in growth and styling.
If you have dry hair, ensure you wet it thoroughly, pour the right amount of shampoo in your hands and apply it well all over your head. Then, gently massage your head before rinsing it well, to remove all of the shampoos.
Use a light conditioner at all times.