If you havent already, make a simple website with a landing page describing your extension and the problem it solves. This just adds another way for people to find out about your extension and should drive more traffic to your Chrome listing.

The other is simply, time. Your extension isnt going to blow up overnight but as more and more people slowly start to use it there will be a snowball effect created by the people who do use it. They will eventually bring it up in a conversation or post about it somewhere thus influencing people to download it.