Make sure the login screen is easy to find

Most sites put more emphasis on registration than on the option to log in. This is understandable; you want signing up to be as easy as possible, and most users with an account are already logged in anyway. 

Make sure there’s no confusion between the two, and make the login screen easy to find. Existing users shouldn’t have to struggle trying to get onto your site. Ideally, your page should have two simple links: “Sign up” and “Sign in”.