How do you wash a backpack without ruining it?

Could you please elaborate on the proper steps to wash a backpack without causing any damage? I'm particularly interested in knowing if there are any specific detergents or techniques that should be used, as well as any potential pitfalls to avoid during the cleaning process. Additionally, I'd like to know if there are any general guidelines for determining whether a backpack is machine-washable or if it requires hand-washing. Thank you for your time and expertise in this matter.