In general:
1. Find a business lawyer and a business CPA (Accountant), have a meeting with your partner, and them, and figure out how you want to structure your business, what the incorporation costs are going to be, etc. ~$500 is a good number for legal fees & incorp. costs, but that varies a lot by state. I recommend the laywer & CPA be in the same room: they usually have different perspectives on things, and so it’s best to get them together.
2. Incorporate—In the US you may end up as an S Corp, or an LLC—LLC’s have changed a lot over the past several decades. Your lawyer will also help with any licenses you may need—that varies a lot by state and locale.
3. Get Advice. Your local business community wants to help you. TiE Global has lots of local chapters, and they’re awesome: https://www.tie.org/ But Rotary Clubs, local business support NFPs, etc. all help.
More specifically:
A. Don’t talk about your product on the internet just yet, but don’t be afraid to talk to people in person. Ideas are cheap, implementation is hard. Chances are someone has had your idea, your goal is to make it happen better than they can. If it’s patentable, you have 1 year from when you announce the product (or “make public”) to file patents, before you lose the ability to. (See “Ideas are cheap”—you may not need or want to go through a patent process—typically patents are $5k to $15k to get.)
B. If you’re developing a consumer product, realize that you’re going to need to have or raise a bit of capital. There’s a lot of testing, certifications, and spin-up time that goes into consumer products, which costs money.
C. Don’t be afraid of marketing. If you don’t really know what you’re doing when it comes to marketing, hire someone who does.
D. Generally avoid hiring family and friends. If you have to let them go for whatever reason (poor performance, bad fit, or downsizing), they’re really hard to fire. If they’re critical to the company (my wife is my CFO), it’s fine. Hiring friends and family for “seasonal” or “overhire” positions is also ok—it’s easy to get rid of them at the end, and they haven’t built their lives around the job.