Designing websites is a lot harder than it seems.  Most companies have a million things they want to tell visitors and there's only room for a few different items on each page.  Hopefully the few things that you pick to put on your homepage are interesting enough that the visitors click through and read more pages so that you can tell more of your story.

There's no right or wrong way to handle a landing page (the first page users see) but there's one principle that I think should always hold true:

Your existing customers are more important than your non-existing ones

From a business point of view, this is might not be true, but it's something that businesses should convey to all their visitors.  Even if I'm not a current customer, I'm more likely to trust your company if I see that you're focused on taking care of the people that got you where you are.

At work we were writing the phone tree that people navigate through to get to sales, account management, etc..  The decision we had to make was between making sales easier by making that the first item on the tree (press 1 to talk to a sales person) or if customer service should be first to reward our existing customers.  The answer was obvious.  Not only are our existing customers more important, but anyone calling for sales would want to hear that we give a priority to customer service above sales.

One main way that companies fail to cater to existing customers is by making their landing page completely sales oriented without making it obvious what existing users can do to access their accounts.

Credit Karma is a site that gets me with this all the time.  Sure they have a "login" link at the top, but every time I go to the site, it's to check my credit score (Why else would I go there?) and there's a huge yellow button saying "Get Your Free Credit Score".  Of course I click that button.  This of course takes me to a signup screen rather than a login screen.

When you go to gmail.com, you see a login area with a link to create a new account.  It would be pretty annoying if every time you wanted to check your email you had to click through a bright flashy screen that ignored the fact that you might already have an account.

I know what you're thinking.  You're thinking, "Tyler, you're really nitpicking here and this is a dumb argument."  Ok, I am nitpicking.  Of course companies want there websites to be sales tools, but I think this mindset infiltrates other more important aspects of how a company does business.  They lose focus of who is most important: Me.