The God Login : how login should be made

The link below has a nice list of design check points for making login dialog box. If you don't want to read the whole article, here is a summary (you can always check the reasons for each point from the original article)

1. Let the user enter an email to log in
2. Tell the user when their email doesn't exist
3. Let the user switch between Log In and Sign Up any time
4. Pick common words (for login and sign up box)
5. Work with browser password managers
6. Handle common user mistakes
7. Help users choose better passwords
8. Don't forget the keyboard (does "tab" and "enter" keys works well on your login form?)
9. Rate limit all the things

Full Article : The God Login: "What's the God algorithm for this?"