Analyze your previous post engagements and the peak time when the audience is active online. Future posts should be tuned based on the analyzed data. In my opinion, video posts are comparatively better at getting more engagement. You have a chance to reach a new audience through Facebook Watch when you publish videos.
Also, create a Facebook group based on your niche and invite group members to like your Facebook page. You can also post on other groups as a page and invite post-liked people to "like" your page. The same can be done with event posts too. They have a high potential to reach new audiences. But doing it frequently may cause restrictions from this feature.
