Send reminder mails to registrants in order to remind them of the webinar. It will allow them to schedule their work accordingly and would help you get the maximum number of people for your webinar.
These paid Q&A webinar sessions can be held weekly or monthly with experts. Leave time for attendees to ask questions to build a quality relationship and fulfill the purpose of your session.
Provide a short video to describe the benefits and what people will learn through your webinar. You can put it on your website, social media, blog and emails.