Developing a prototype based on an Arduino,or other development kit, is a great first step.But if you want to make your product into something that can be mass-produced and sold to the masses, there's a lot of work to be done.
Step 1-Design the Microcontroller Circuit
The Arduino is a microcontroller development kit, so the first step is designing a custom microcontroller schematic to replace the Arduino. And the first step of designing a microcontroller schematic, is to select the microcontroller.
Step 2-Design the Schematic Circuits for Any Shields
schematic exampleNow that you have your core microcontroller schematic circuit designed the next step is to design the circuits for any Arduino shields you may be using.
Step 3-Design the Printed Circuit Board (PCB)
Once you have the full schematic circuit designed for your product, the next step is to turn it into a real world Printed Circuit Board (PCB).
Step 4-Order PCB Prototypes
Once you have the PCB layout completed it is now time to order the PCB prototypes.In many cases you'll use one vendor to produce the blank PCB's, and another vendor to solder all of the components onto the board.
Step 5-Develop the Firmware/Software
Now it's time to port over your Arduino code to native firmware code for the microcontroller selected. This will be considerably easier if you are using the same microcontroller family as used by the Arduino model you used.
Step 6-Rinse and repeat
Regardless of how careful you are, or how good of a designer you are, you will almost surely find at least a few problems with your first prototype version.If money is not in short supply, the fastest way to develop new products is to prototype early and often.