Decide what you need to validate
Is your prototype intended to prove a core function, evaluate usability, or test a manufacturing approach? Its purpose determines the level of finish and development scope required.
Build a smaller version and learn
Validate the most important function before implementing every feature. Use the limitations and changes discovered during testing to guide the next design.
Plan the path to a product
A working function and a product that can be repeatedly manufactured and operated are different stages. Review durability, assembly, maintenance, and operating conditions separately.