There is no definitive answer to this question as it depends on individual preferences and hair type. Generally, people with oily or greasy hair may use shampoo more often than those with dry hair.
If you have oily or greasy hair, it is recommended that you use shampoo every time you take a shower. This will help remove the excess oil and keep your scalp and hair clean. If you have dry hair, using shampoo every time you shower may strip away the natural oils from your hair, leaving it dry and brittle. In this case, you may want to use shampoo every other shower or every third shower.
When using shampoo, the amount you use will depend on your hair length and texture. For shorter hair, you may need to use less than you would for longer hair. If your hair is thick, you may need to use more than you would if your hair was thin.
In addition to shampoo, you should also use conditioner. Conditioner helps to lock in moisture and nutrients, and it also helps to make your hair more manageable. You should use conditioner every time you shampoo, but you don't need to use as much as the shampoo.
Overall, it is up to you to decide how often you use shampoo and conditioner when taking a shower. It is important to take into consideration your hair type, length, and texture in order to determine the best frequency for you.