In my opinion it is quite simple, really. Do not build a product. Build a solution to a problem. There's a huge difference! People don't buy gadgets, they buy something that solves a problem for them. So:

1. Figure out what problem needs solving
2. Build something that solves that problem in an easy-to-use way
3. Tell people about your solution
and Bonus:
4. Sell accessories and accoutrements to enhance the solution with your solution as the centerpiece purchase.

As for the specifics of how to choose technologies, how to manufacture, how to product develop, I can give you hours and hours and hours of advice on those. You just need to tell me what exactly you want to find out about. ;)