How to create a subnet mask?

Could you elaborate on the process of creating a subnet mask, please? I understand it's a crucial aspect of networking, but I'm not entirely sure how to approach it. Could you provide a step-by-step guide on how to determine the appropriate subnet mask for a given network? Perhaps explain the role it plays in segmenting the network and how it affects IP addressing. Also, are there any best practices or considerations to take into account while creating a subnet mask? Your insights would be greatly appreciated.