When bathing a dog a dog only needs bathed once per month or every 4 weeks.
Once per month which is every 4 weeks is good enough when bathing most dogs.
Bathing the dog too often can strip the dogs skin and fur of natural oils and dry the dogs skin out and could make the dogs fur fall out more.
However if you do need to wash or bathe your dog more often than ever 4 weeks because the dog gets muddy or dirty then it's okay to do so.
Use a good dog shampoo that is formulated for the dogs fur and skin.
Using human shampoo is okay if it's all you have and you need to bathe the dog but dog shampoo is much better for bathing the dog with.