It’s paradoxical… we humans are creatures of habits, yet it can be hard to form new habits. Here’s one thing I found useful: (1) deciding to do something regularly (e.g. daily), (2) tracking how many times in a row I did this. The motivational trick is trying to create the longest chain; if I fail to do whatever I’m tracking, I start at zero.
Now, the first step is important. It’s about a concrete, measurable goal. For example, do more reading doesn’t work; read one paper every Wednesday is. I found that less is more here: being too ambitious is more likely to lead to breaking the chain or just fatigue and motivational lows. By contrast, doing a little every day, or once a week, does add up… What is more, I schedule different things according to my week: weekends and weekdays are different, and days I spend commuting are different from days working from home.
For the second step, I also have clear rules (which vary according to the goal). For some, it’s every day, no excuses. For many there’s a list of acceptable excuses. For example, if I have to work later than a certain time, I allow myself to pick one of the remaining chains only. Or, for some goals I allow myself to skip once a week. I find these acceptable excuses useful to maintain the motivation of tracking chains, yet being able to adapt to real life. That said, I only permit one acceptable excuse in a row (irrespective of goal tracked).