Dive summary:

• Landing pages are the internet's version of a billboard, but with the added ability for the user to take immediate action.   If the user can't understand what the page is about in 3 seconds, then you have failed.  With this in mind, make sure your page is simple and has a sole purpose.  The headline should be big, bold, and easy to understand. 
• Show testimonials or numbers, and -- *Ryan grabs your shoulders and shakes* -- have a clear call to action!  Users need to know what to do next.  Whiffing on a good call to action is the cardinal sin of landing pages.
• Lastly, pictures and graphics shouldn't be solely for aesthetic appeal.  They can help guide your user.  For example, studies have shown that having pictures of a person looking at the call to action can increase clicks. 
• There's more good stuff, including visual examples, if you click through on the article below from onextrapixel.

From the article:

So you have spent loads of time and possibly money driving traffic to your awesome site selling your products or services, but you aren’t getting enough leads. Your website is drop dead cool and your products are definitely worth buying, so what’s the deal? Well, it means that your conversion rate is low, which you already know. This could be a result of a number of things.

Visitors may not know how to buy your product or service, they may not know exactly what you do, or they may simply just need you to tell them what they need to do in order to acquire your services. How do you fix this problem, you ask? You, my friend, need a landing page.