Ask HN: Browser plugin install rates?

Hey from a first time poster, my new website is now in beta, and needs users to install a plugin..

Right now we get around 30% install rate for those who want to register (doesn't count the people who may be put off and don't register because of the plugin).

Any others out there using plugins can share their thoughts about how to raise the rate?

Any best practice examples?

Thx (from a first time poster)