Easiest thing for me is: HABIT 3 - View problems as challenges.
I love problem solving and work best under pressure. That comes from all my years in computers and programming where whenever something was not working it had to be fixed yesterday.
Hardest thing: HABIT 1 - Start with the end in mind.
Goals keep changing so the end is often actually the beginning. Goals are based on experience so as you evolve so do your goals. Sometimes the best goals or achievements turn up in unexpected ways that you can miss if you define your quest to narrowly.
Keep your eyes on the path ahead BUT don't forget to look around you while you are on the path.