The best way to do so is by extending the reach and lifecycle of the content and getting it in front of attendees and non-attendees, alike. This will give you a second chance to reach registrants who didn�t attended the webinar for any reason. It helps create high quality content for your webinar and makes webinar replay effective.
If you have a company blog, it can be the best place to announce your webinar. Through blogs, you can target your audience by discussing how to register for the webinar and the webinar content itself.
You can involve sponsors in your webinars to make money from sponsored ads and announcements which run in between of your webinars. It can be very beneficial when you are attracting larger audiences through your webinars.
It is really difficult to get an audience to be a part of your webinar. You always need to look for a topic from your niche that is trending to be able to capture the attention of a large audience. Do some research and look for customer problems. Be relevant and informative with your webinar topic to encourage more people to attend your webinar.