As Search Engine Journal said, "With hundreds of billions of webpages in Google’s index, you need to optimize your crawl budget to stay competitive."
You should be checking your website's crawl status at least every month or two. Check for errors and make sure everything is functioning properly.
Mobile-friendliness is also really important for indexation, as well as regular content!
Have you submitted a sitemap? This is a really important step that can definitely make a difference.
Click the link for more great indexation ideas!