I usually start with a keyword but make sure that the title makes good sense in full. In case I target several keywords on a page - I`m selecting the most winning one, and think of a title most answering to that keyword as a search query, so that the result would look really appealing for users (I`m a strong believer that CTR matters once you rank high). Therefore I focus on optimizing how the search result will look on the whole, together with the description and structured data markup if possible. Truncated titles also never look good, so I stick to the limit of 50-55 characters.
