What is your “why?”
What do you want from life? How will losing weight, finishing the triathlon, going on that hike, or simply having more energy make your life better? Establishing your why is essential to forming new, healthy habits. All change must start from within. The mind is extremely powerful and will win most internal arguments (see what I did there).
Where does your motivation come from? Really own this answer. It will help keep you on the path.
Think small. Look at your priorities and define short-term realistic goals. The change will be incremental, so start with one habit, work on it day by day until you own it. Move on only when ready.