How to plan a website, with dependency 80% on google organic search and 20% direct users?
Please share your views, knowledge and experience...
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Easy. Ensure the site is relevant and useful to those who search and type to land on your site.
OK, it's a overly simple and slightly haughty answer, but its true. If the majority of your users are coming from search engines, then the landing pages should be tailored to their searches so they aren't annoyed by irrelevant content and bounce/leave.
Direct users are less of an issue, because most direct users will land on the home-page and will be knowing what they are looking for or have been to the site before.