Excellent question, there's a couple factors that must be first addressed to give you the most effective answer:
-Are the 75 participants loyal, returning guests or are they generally new faces?
-Do you offer upsells at this event? This opens the potential to reduce ticket door revenue to increase profit from back room sales?
-Do the events revolve around themes? This would allow you to generate consistent attendance and have guests bring friends to also implement this bi-weekly theme.
As a first step, I would try to get a very good understanding of these things from the people who attend one or more of your next three events: what they like somewhat, what they like strongly, what they don't like somewhat, and what they hate about the event. Basically a 2*2 matrix of like-dislike on one axis, and weak-strong on the other axis.
Some strategies may come out directly from building this understanding.
A couple of thoughts:
First, consider a smaller venue - say for about 80-85 people. This will make the event seem "bigger" to new attendees and help you generate some buzz about it being well-attended. A large, empty space that's half-full creates the opposite impression - even though 75 people is a really decent turn-out.
Second, I'd put the question of how to increase turnout to your attendees via a web survey asking whether they would recommend the event to other entrepreneurs that they know and why/why not. This gives you a net-promoter score that you can use to gain some insights on what folks find most valuable which in turn can be used to target new attendees.
Great question, by-the-way. Good luck!
It is important to ensure you communicate the value of your event and what people will get from their investment. Then you have to over deliver. Next, you have advertising your event more than you probably want to--especially on social media. You have to figure out when your audience is online and make sure you're online promoting your event while they are there. For most entrepreneurs, early mornings and late evening seems to be their time. Hope this helps!
When I support organisations live events, I always start with some questions around their objectives. I'd start by asking why you are thinking about "doubling attendance"? Is this really the best objective to be chasing? I often find the best events, from a supplier and an attendee perspective, are about quaility and not quantity.