Let's take facebook and google+ homepage for example. According to you what makes them great or what improvement they need?
for example if you have a holding page then a call to action to register your interest and the reason why you would do so are the priority.
for a generic landing page for your new users you need to think of origin
if from a google search then there is something the page that interests them, find out the search term and if in line with your businesses goals/product then make this information clear and leading into your product.
if its from recommendation i.e. 'hey steve visit x' then you want your landing page to explain what you do as clearly as possible, then a call to action for their most requested event e.g. how much does it cost, where do i register