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Since you're the one with the idea for the product in the first place, you'll be the first line of testing. Try out your product on your own and see how it works. Keep track of little frustrations, elements of the product in need of tweaking, and spend a good deal of time using and thinking about the product you're testing.  As you use the product, keep a journal or a voice recorder with you to keep track of your experience of the product as you're using it. You might tend to remember all the bad or all the good later on. Don't just use the product, abuse it. If you're thinking about going into production, you'll want to find out what your product is made of, and whether or not it'll stand up to people throwing it around, dropping it, and the other trappings of real-life ownership. Is it fragile? Could it use some reinforcing? . This is one of the most important parts of developing a product. Who's going to buy what you're selling? Who, like you, will have experienced the same frustration or desire that this product will fulfill? How will you reach that audience? The next step of your process will be getting other people to use your product and give you feedback, so you want to define your audience as specifically as possible in terms of several criteria:   Age range Socio-economic status Level of education Hobbies and interests Prejudices and opinions Bring your product to a group of people, let them try it, and give them the opportunity to provide feedback. This could be as informal as giving a few cases of your home-brew to your friends and family and listening to them review it, or as formal as doing a serious focus-group session with a series of different test groups.  If you want to do an informal feedback session, treat it as seriously as the product warrants. Your parents and your friends will likely tell you that your new beer is "Delicious" to be nice, but also give it to some serious beer drinkers to find out whether or not you've got the stuff. If you conduct formal focus groups, do several runs with different groups of people. Your audience may be slightly different than you originally anticipated. Listen and gather feedback. As you give your product out and introduce it to unfamiliar users, start collecting first-hand feedback. Write up surveys, conduct interviews, and listen closely to the feedback given. Often, the difference between products that catch on and products that fall by the wayside is the ability of the inventors to incorporate feedback into product development. In some cases, you might find it more effective to allow someone else to gather feedback about your product from testers. You may be inclined to defend your product against criticism, whereas a more unbiased researched will have an easier time collecting this feedback. Steve Jobs wasn't a renowned inventor. He was a genius tweaker. The best products aren't usually the result of great leaps forward, but of little changes that make a good innovation or concept into a great product that you can sell. Incorporate the feedback you receive about your product into tweaks and revisions that will take it from good to great. The feedback you gather will likely not have great ideas about ways in which the product needs to be changed, but you can listen to the criticism that occurs and come up with your own ideas about how to address those complaints. So people found your book prop somewhat complicated to use? How can it be easier?

Summary:
Use the product yourself. Find an audience Do a series of test trials. Gather criticism. Revise the product.