Make sure you are registered with the correct tax offices for your location. Where I am, you have to register at the federal and county level (the county communicates with the state). If a brick and mortar business, then I would assume you also have to register with the city, but I don't know.

Also, make sure your policies are explicitly written. Preferably multiple times. And maybe even verbally going over them....some clients need more "direction" than others.

If your business is multistate or multinational, make sure you know the laws there! Most US states have minimum limits before you have to pay taxes. Every country has their own policies on these things and paperwork to fill out (some easier than others). There are companies that will collect and remit taxes for you, which can be extremely helpful especially as a small business in multiple jurisdictions.

Also, different jurisdictions have rules about what can and can't be sold. Sanctioned countries, rules about children's toys, varying levels of legality for different substances and materials...just things I can think of off the top of my head.

It can get overwhelming and business/contract lawyers are underrated and not as expensive as someone might think (depending on what you need).