Your attorney' accountant's, etc. if you use them should be guiding you on how to get set up with different things.
Some things that you should expect to encounter is of course organizational setup of corporation, LLC, proprietor....basic accounting and how to set up to make it easier for income tax filing time.
Things that you may not think about that they hopefully bring up or can come up at some point:
Registration for a Federal Employer ID - if you are a proprietor and have no employees you don't necessarily need one - your SSN is usable anywhere you would otherwise use a FEIN
Registration with state department of Labor - may not apply everywhere, but chances are there is some equivalent agency you will need to register with, especially if you employ others, you will likely have to file unemployment tax returns of some sort with them. They will catch up with you eventually if you don't do it and demand you file past returns and pay whatever tax would been due plus penalties.
Payroll taxes if you have employees
Sales taxes - even if you don't have to collect and remit sales tax, many times you still at least need to be registered with said tax agency and file paperwork with them that indicates your operation is in a position that it doesn't need to collect and remit such taxes. Some cases you maybe tax some things but not others as well. They will also eventually catch up with you if you don't do it so just check into it from the beginning and make sure whatever you are doing is the right thing to do.
Insurance - general liability, coverage for your tools and equipment, make sure you know what is or is not covered - if you rent say a backhoe or scissor lift it may not be covered by your equipment policy, rental places often offer insurance or some even require you purchase it unless you can show your regular policy covers it.
Insurance - workers comp - if you have employees, or maybe even coverage to include yourself if you are set up as an employee of the company.
Setting up yourself or even your spouse as a paid employee can allow you to pay employee benefits to you or your spouse, a big one is health care insurance and expenses. Probably best to talk to your accountant on how to proceed with any of this.
You can take major depreciation amounts as deductions on income taxes particularly when you first start up a business, and then as you purchase tools, equipment, vehicles, etc. That helps reduce taxable income, but if you borrow money to purchase such things it does add to your debts so don't go overboard with purchasing things just to reduce income tax, sooner or later you have to pay either taxes or loans, or some of both- keep it balanced to what you need to keep operating.
Something else you might run into, might vary in different places as well, is that stuff you take depreciation expenses on for income tax, often wil be subject to a local "personal property tax" or similar. If that applies they also will eventually catch up with you if you haven't been filing it.
