Do you sell first or comply with laws/tax first?

It is a jurisdiction specific question. In some places you need license(s) just to operate as a business.

In most cases it is better to incorporate and do all the necessary registrations before making sales. But if your product/service doesn't take off as expected then the up-front costs are in vain. Some persons are comfortable with the risks of operating as a sole-trader.

Comply with tax and other laws first. To do it the other way around is, in my opinion, completely unethical. Even ignoring that lawbreaking makes the company literally a criminal organization, a willingness to do that indicates a kind of fundamental flaw that makes the business forever untrustworthy to me.

Comply first. Otherwise, you won't have a business bank account where you could direct the money from the first sale.

It probably doesn't matter if you're a beginner.