Be sure the requirements are clear and concise. The more information you are able to provide the easier it is for your supplier to meet your needs.
If your clients requirement seems ambiguous, ask questions to clarify the goal of the end product. Such as; How will the product be used/implemented? What does the seller with want the consumers impression of the product to be? Who is the target market? What will discriminate this product from that of the competition?
Pictures are very helpful especially if there is a language barrier. Not everyone calls a “widget” by the same name!