Immersion means 100% focus. If possible, no friends, no drinking, no TV, just reading and writing code. If you take five minutes off to read the news, be aware you are breaking the mental state of immersion. Stay focused, be patient, your mind will adapt. Eliminate all distractions, of which you may find doubt to be the loudest. Immersion is the difference between success and failure.
With cover letters, the main reason for rejection comes from the fact that people just send generic resumes. They don’t show an interest in the company itself. The same thing goes for your resume. It needs to be tailored to the company.