Shampooing probably every day if you have oily hair, and once a week if you have coarse hair is a part of taking good care of yourself. If a boy uses hair gel, he will have to wash his hair before bed. If your hair tangles easily, especially if it’s long, you can use a special conditioner.
To prevent dandruff if you have especially dry hair, you can get a special shampoo for that. If you swim in chlorinated water, like in a swimming pool, you can use the same shampoo.