A modo de resumen incluyo en este artículo, los errores más típicos en el diseño de páginas de registro sacados de Account Sign-in: 8 design mistakes to avoid y Account Sign-in: 8 more design mistakes to avoid.

Voy a hacer un copy-paste, para que sirva como referencia:

Mistake #1: Having a Sign-in In The First Place
Mistake #2: Requiring Sign-in Too Soon
Mistake #3: Not Stating the Benefits to Registering
Mistake #4: Hiding the Sign-In Button
Mistake #5: Not Making "Create New Account" or "Forgot Your Password" Link
Mistake #6: Not Providing Sign-in Opportunities at Key Locations
Mistake #7: Asking for Too Much Information When Registering
Mistake #8: Not Telling Users How You'll Use Their Information
Mistake #9: Not Telling Users the Requirements for Username and Password Up Front
Mistake #10: Requiring Stricter Password Requirements Than The NSA
Mistake #11: Using Challenge Questions They Won't Remember In A Year
Mistake #12: Not Returning Users to Their Desired Objective
Mistake #13: Not Explaining If It’s The Username or Password They Got Wrong
Mistake #14: Not Putting A Register Link When The Sign-In Is An Error
Mistake #15: Not Giving the User A Non-email Solution To Recover Their Password
Mistake #16: Requiring More Than One Element When Recovering Password