Devise, customizing the error messages?
<% if @user.errors.any? %>
    <div id="error_explanation" class="error">
    <h2>Hold on!</h2>
        <ul>
            <% @user.errors.full_messages.each do |msg| %>
                <li><%= msg %></li>
            <% end %>
        </ul>
    </div>
<% end %>

Email The User's Email cannot be blank
Password The User's Password cannot be blank
Fname The User's Fname is too short (minimum 1 characters)
Lname The User's Lname is too short (minimum 1 characters)

validates_presence_of(*attr_names)

 Configuration options:
  message - A custom error message (default is: "can‘t be blank").

activerecord:
   attributes:
       user:
        email: "your_way_of_email"
          password: "your_way_of_password"
          password_confirmation: "your_way_of_password_confirmation"

<% if @user.errors.any? %>
    <div id="error_explanation" class="error">
    <h2>Hold on!</h2>
        <ul>
            <% @user.errors.each_key do |attr| %>
                <% @user.errors[attr].each do |msg| %>
                    <% next if msg.nil? %>

                    <li><%= msg %></li>
                <% end %>
            <% end %>
        </ul>
    </div>
<% end %>