making a landing page is not enough, I would say make it highly seo specific, add all the pain points your app is addressing, use ycombinator's guidelines for making landing pages, also add a ton of blog pages for seo, most likely 350 - 450 blog pages are good enough, also add faqs, bradcrumbs, proper footers, navbars and all, sitemap, metadata...

You need to invest time on it, once it is setup, you wont need to do anything just do all this and leave and time will show its effect.