You're familiar with the term "premature optimization", right?
Don't bother forming a corporation, renting office space, or even making business cards when you don't have any customers or revenue.
It's perfectly acceptable, and the recommended approach, to simply operate as a Sole Proprietorship (no legal entity for the business, just self-employed income for you) until you have a REASON to form a corporation -- things like, to mitigate liability, to hire employees, to take on investors, etc.
As a sole proprietorship, you can still do business under a company name - this is called DBA, "doing business as". So if you go to get a business bank account, for example, you can open the account under the name "Firstname Lastname DBA MyCoolInternetCompany". You can also get an EIN or TPIN (employer ID number, taxpayer ID number) from the IRS without an official business entity.
Later on, once you have customers and revenue, you can then form an LLC for a few hundred bucks depending on which state you are in. You can do this first, of course, before actually starting your business and getting revenue/customers, and many people do -- but it's a common mistake for new entrepreneurs to focus on the fun/exciting stuff like making business cards etc instead of the boring but critical stuff like, you know, actually making money.