Patent searching by keywords typically means searching for keywords in the abstract and/or full-text of the patent.
A robust set of keywords should be brainstormed before you search. As you search, this list should be reviewed and updates as new search results surface new keywords.
To start off, think about:
- synonyms
- broader terms
- narrower terms
- related terms
Also, think about where truncation and search operators (AND / OR / NOT) may be useful.