How do we make rules?

[Moneypenny]

I've been trying to read up on making rules, but have had a complete blank in where to begin.

I'm looking to write rules (with my husband) for ourselves as a couple as well as rules regarding a secondary partner if/when both or one of us has one or more.

Can anyone just let me know what kinds if rules you have and how they've worked for you?

Thanks!