Don't Make Me Think... About Your Code

"Don't Make Me Think" is the title of the famous UX book by Steve Krug. One of the main ideas in the book is that a user interface should be designed in such a way that users' thinking is kept to a minimum. As much as possible, it should be obvious what actions the user must do to achieve a goal. Answers to questions like "where do I go to checkout?" or "what will happen when I click this button?" should be obvious just from looking at the page.