1. Brainstorm keywords related to the purpose, use and composition of the invention.
2. Use Patents in Engineering Village to search your keywords; gather preliminary U.S. Classifications by reviewing the abstracts and classification definitions from the patent records; examine the claims and drawings from the full-text of patents; examine patents under the links, “Patent Refs” and “Cited by”, for relevancy. Examine citations under the "Other Refs" for relevancy. (keyword indexing starts in 1976)
3. Use the U.S. Classifications you gathered to search Patents in Engineering Village by classification number (indexing of class numbers goes back to 1790). Review the abstracts, claims and drawings for relevancy. Check all references and note the U.S. Classifications and “Field of Search” areas for additional class/subclasses to search.
Seven Step Strategy (USPTO)
How to Conduct a Preliminary U.S. Patent Search (USPTO, Video)
Prior Art Searching
Prior art searching includes more than searching patent databases, but requires checking the journal literature, dissertations, conference papers, eprints, the Web and advertising sources for any previous description of the invention. Examples include Summon for a published literature search and ThomasNet for product advertising.