What business types have to follow strict procedural requirements?

There are no formal procedure requirements which sole proprietorships have to follow, which is why they are these easiest type of business to run. Partnerships and LLCs have some limited formalities they have to file, as mandated by state law, although there are generally no requirements for things like annual meetings. Most states have very strict formalities which corporations must follow, including the fact that they generally must hold annual meetings of their shareholders and directors.