Quality content and quality promoting
Content:
Posting consistently based off the demographics of your audience and the peak times for the best engaging activity possible
Don't post too often, make sure your post gets time to reach the audience
Try to be original
Put effort into your content
Make sure your content relates to your page and your audience
More engagement = more trendy
Promoting:
Shout outs perhaps. These will cost you but at least only people that like your page will follow you
Do not buy fake likes or fake followers - these will decrease your reach of the posts
Do actions which require the audience to like, share or comment - this will increase the reach of your post
(This is why you need engaging content)
There are maybe more details but these are the most important
Also, most people give up shortly after their motivation runs out because of high expectations