1.- Get a domain.com to look more professional otherwise if I see "GitHub.io" looks like a code repository Pick a better name for your product. Right now it doesn't mean anything (i.e. dropbox reminds people of storage, submittable.com also sounds like form management, hope you get the idea)
2.- Look at well designed websites (i.e Invision, xero.com, mint.com. stripe.com) and notice the difference.
3.- Copy. There's zero copy. Check mailchimp.com for great voice and tone.
4.- No Pricing info, policy, FAQ, etc.
5.- A short 1-2 minutes explainer Video (optional)
6.- Look at well done explainer videos
7.- The landing page doesn't necessarily have to be all flashy, check this one for a simple one: https://visualping.io
8.- Important: Get feedback from people, I've used this: https://userinput.io/
9.- Also, forget HN, PH, etc., go after offline people or try more creative ways to reach people directly.