Quick items:
Register your DBA (doing business as) name if different than your own name.
Make sure you business does not violate any zoning laws.
Get a federal and then a state tax id. (Call the IRS -- many states require you to file for your fed id first).
Get all local and state permits. For internet services there are currently no national level (in the USA at least) permits that you need (or at that I now you need

) For example, we are required to have a sales-tax permit for our state despite our services being non-taxable. I fill out forms every 3 months with zeroes in them.
Tips
Pick up a book on the topic. Nothing fancy -- just one that covers the basics. Many have example forms that you need.
Make sure you have your finances in order --- get seperate accounts for business vs. personal. If not up to it, get an accountant to help you setup your books initially. It is far easier and cheaper to do at the beginning that a year or two later. Especially, when dealing with partership or LLC formats.
Consider a SP-LLC if your state allows it. Slightly more difficult to get going but limits your liability to just the business at does not pass through to you.