On Medium, you need to focus on the entire title block. Always compose a complete block – that's the kicker, the main title, and a subtitle. The kicker is kind of an extension of the topics tags; it's almost like a sixth tag to the algorithm. The main title needs to grab your reader, but try to keep under around seven words (try to never use more than ten words). Your subtitle should continue the theme of your main title, but can be longer – just keep it under two lines.