Habits are a powerful way to invest willpower. You put in a medium amount of effort to create one, a small amount to maintain it, and then you benefit continually. For example, I built myself a habit where at lunch at work after filling my plate with what I want to eat I put vegetables on top. Before this I didn't eat vegetables often but knew I ought to. Occasionally I would get myself to eat some, but I didn't have the willpower on an ongoing basis to do this significantly. Now that I have the habit trained up, however, it takes me nearly no effort to follow it. It's just what I do now.

Other habits I've trained:

• I keep a bottle of water at my desk, and when I see it's empty I have to fill it immediately.
• I leave instruments out where I'll see them and play them.
• When I notice I'm thinking "remember to do X at time Y" I set an alarm on my phone. When I notice I'm thinking "remember to do X on day Y" I send an email to [Y]@followupthen.com.
• When I'm in the shower and notice that I'm done cleaning and just enjoying the warm water, I start counting down from ten. When I finish, I immediately turn off the water and get out. It's much easier for me to promise to get out in ten seconds than to get out immediately.
• Every time I spend any money I write it down.
• There's a tree branch I walk under on my commute, and whenever I pass it I'll do a pull up on it. At some point I'll invest the willpower to switch to doing more. Actually, as of now, my habit is that I do two of them.
• I do stretches and exercises for my knees every night before I go to sleep. (This one is boring enough and long enough that it takes willpower to maintain it, but still much less than before it was a habit.)
• At work, my desktop is only for working. If I want to do something personal I have to get out my laptop and do that there. I used to categorize unimportant-but-work-related things like reading company-internal mailing lists as ok for the desktop, but after a discussion today I see they should go on the laptop.
• I use my desk at work both sitting and standing, switching between the two for comfort. Whenever I leave my desk, I switch it to standing position for when I come back.

When I'm considering making an exception to a habit, I think about it not in terms of the downside of failing to do it just this once (which is of course small) but the downside of not doing it in all future cases where I have an excuse at least this strong. This downside usually is large enough that I just keep up the habit.

(I also have other less interesting habits, like charging my phone, putting my wallet in my pocket, and brushing my teeth.)