Umm - by making it and selling it?
Ok - that was in jest - but it comes close to the truth.
Basically - you don't just want to make and sell any product, but you want to also sell/provide something to your clients that will differentiate your offerings from the competition in order to build your brand. You'll want excellent customer service. You'll want a way for your customers to interact with you and your products (ie, reviews, forums, comments, blogs, the whole social media thing, etc). You'll want your products to be sufficiently different or "niche" compared to offerings elsewhere. Anything you do that is similar, you want to be better (verifyably and identifyably better) - whether that means better construction, more reliability, better performance, different approaches.
Something you probably don't need to worry about as much is "whether your competition will steal your ideas for themselves to sell"; your main competition being "China" of course...
Whether it is open-source or closed and heavily proprietary (with patents and copyrights) - someone is going to appropriate your design and sell it; your only hope is better marketing, quality of product, and customer service.
...and even all of this may not be enough for you to do much better than break-even, if that.
That's business, unfortunately.
So - get out there and do your research; look into the whys and hows the Arduino has become a phenomena. Search out and review SparkFun's site. Research AdaFruit, RuggedCircuits, etc - and see what they are doing and why they are successful. There are tons of "open source" hardware companies out there. Think about what you intend to sell, and how you'll sell it. Think about what you can do to make your product more unique and appealing to the customer. Think about how you'll interact with that customer, and what products and services you can offer them before and after the sale to get them to talk to come back to your brand again, and let others know about your products. Think about how you'll deal with problems customers have with your products (because they -will-), and how you will solve those problems while keeping them a customer (if you do this well enough, you might get them to recruit others simply because of "great customer service").
Starting a business is a huge undertaking to do right; if you just "jump in" without giving it the proper thought and time for research, you'll likely sink more often than swim (unless you're one of the lucky few entrepreneurs who are able to do just that - if so, good for you and good luck!)...