Test Your Ideas Quickly, Prototype
Having some action taken to get the feel of the product you want to make is a fundamental step before risking too much. As it happens in architecture and other creative fields, early prototypes help judge ideas, discarding bad ones and pushing forward the best ones.
The best way to have great ideas is having lots of ideas. — Linus Pauling
Ideas are just ideas. An idea can be formalized in many different ways. This is why, even though you have a concept to start with which is valid does not mean you are going to shape it in the correct way in your first try.
Iterate, abstract problems into small decisions which can be taken independently. For instance, if you are designing an appliance, two separate decisions could be its material and its shape. Even though one decision may affect the other, you could decide one ignoring the other. Abstracting problems makes evident which decisions need to be taken in order to move the ball forward.
Design methodologies do not work the same for everyone. But trying other people's processes of design can help you find your own. What do you think?