9 Most Common Mistakes in Landing Page

Have just one call to action
Focus on your USP - compare your product with competitors
Show Social Proof - testimonials, ratings, awards etc.
Simple Language - no technical terms or acronyms.
Pain/Agitate/Solve - show the pain that the product is solving - and agitate it by using vivid emotional language and stories.
Show use cases, benefits
Call to action with context and expectation setting. eg. Buy the product, its just 5$!. Sign up, it will take you just 2 mins.
Add an Exit Intent Survey(ask the visitors why they are leaving/not doing the CTA)
Measure, Track. Setup Analytic

Advanced Ideas

Have niche landing page - target specific personas. Have multiple landing pages for different personas if need be.
Ask it too big or too soon. Make a list of what a visitor would need before signing up. Make sure this is available before the CTA
Show - don't tell. Use screenshots, demo, etc rather than text blocks.
Address doubts. Find common questions(exit survey, user testing) - answer them in site/FAQ.
Regular Conversion Testing