Resist the impulse to add things. When it’s obvious in testing that users aren’t getting something, most people’s first reaction is to add something, like an explanation or some instructions. The right solution is to take something away that is obscuring the meaning, rather than adding yet another distraction.
Don’t make me think
Being an expert in online usability Krug gathered his experience in a wonderful book. This summary of key thoughts will help you to remember most important principles and laws.