Grab the low-hanging fruit. First, when the problem and the solution were obvious to everyone the moment they saw the first user try to muddle through, you should fix them right away. Second, try to implement any changes that require almost no effort, or require a little effort but are highly visible.
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.