You get things done and solve problems best when your mind isn't distracted.
David Allen's book, Getting Things Done, pointed out that the mind isn't very good at remembering important things or making difficult decisions. Rather, when it has to, it devotes more attention to those tasks than you want it to.
For example, say you want to read a chapter of a book and want to remember to call someone important immediately after. Part of your mind will distract your reading by saying "Don't forget to call Jim when you're done... Don't forget to call Jim when you're done... Don't forget to call Jim when you're done..."
You probably learned to write things like that down, which can free your mind. That's why we write lists--to free our minds from trying to remember.
Making decisions occupies our minds too. What you habitualize and systematize you don't have to decide, which frees your mind.
I shave Mondays and Thursdays, for example. Is it a big deal? No. Something to be proud of? Not really. But I never worry about whether I should shave or not.
Two benefits: my mind is free and I develop the skill to free it more in the future.
On a bigger scale, I used to try to decide if I should take the elevator or stairs to my apartment. It's easier to take the elevator but healthier to take the stairs. I'd wonder, as I entered my building which I should do that time. Sometimes in the elevator I'd think, "I'm too lazy. I should have taken the stairs," or in the stairs I'd think, "I did a lot today. I earned an elevator ride."
Switching to always taking the stairs removed that distraction.
Freedom from distraction
The point here is distraction. The problem isn't that that decision was difficult. It's simple, like remembering to call Jim after reading the chapter.
The problem is the mind devotes too much attention to it. The problem is the other important thoughts you could have had or that you do have that your mind disrupts for something less important.
Having to decide whether to go to the gym or not is distracting. Choosing once and for all to exercise at home every day no matter what is freeing. I've decided a minimum level of fitness I accept for myself, how to do it, and now my mind is free of that distraction.
I have tons of little routines and ways that I do things. Some people think they make me geeky. But they aren't about little rules, nor inflexibility. They free my mind.
It's not hard for me to decide if I should clean my desk. It frees my mind more to clean it every night before I go to sleep. I could save time by not cleaning it sometimes and it might not get that messy, but I've found it more distracting to deal with that voice saying "It's time to clean the desk" when I'm busy doing something more important.
A side effect of choosing little things once and for all is enabling yourself to make bigger decisions once and for all.
A friend often invites me to his department lunches. I like a free lunch, but it's not as healthy as my home cooked lunches. Since the lunches are on the 11th floor of his office building, I take the stairs to partly balance the calories.
I don't think about it, I just do it. I'm not particularly proud. I like the exercise, but I don't consider it an achievement. I enjoy the lunch more, free of mental distraction.
Climbing to the 11th floor is harder than climbing to the 5th, where my apartment is. The smaller decision enabled the bigger one.
So I can think about what I want
I have greater priorities than deciding what days to exercise. I'm writing a book, articles for Inc., articles for journals. And creating marketing plans and things like that. I'm teaching. And so on.
Systems and habits make my book and other important things in my life better.
They'll do the same for you.