A practice does not become a practice through dramatic resolution. It becomes a practice the way a path through grass becomes a path: by walking on it again, and again, and again, in the same place.
Same time, same place
Pick one time of day. The most reliable is first thing — before the inbox, before the phone, before the day has any opinions about you. Five minutes. Same chair, same cushion, same spot on the rug.
The mind will resist. It will tell you tomorrow would be better. It will tell you that you have only four minutes today, so it is not worth it. Sit anyway. Four minutes counts. Two minutes counts. The streak is not the point — the return is.
When you miss a day
You will miss days. Most people, when they miss a day, also miss the next day, and the day after that, because some quiet voice inside them says: well, the streak is broken now. Notice that voice. It is wrong.
Miss a day. The next morning, sit again. That is the whole repair.
When it gets boring
It will. The novelty will run out, probably in week three. This is normal and also necessary. The novelty has to die so that the actual practice can begin. What comes after novelty is the quieter relationship — less exciting, more honest, more lasting. Sit through the boring weeks. The good ones come back.
When to lengthen
After a month of five minutes most days, you may notice you want a little more. Try ten. Then fifteen. Twenty minutes a day, for most people, is a life-changing practice. Forty minutes is something else entirely, and not necessary unless you are drawn there.
Do not lengthen before you are reliably showing up. A short consistent practice beats a long abandoned one, always.
Going further
If you want to deepen, eventually find a teacher and a tradition. Not because you cannot do this alone — you can — but because at some point, having someone to talk to about what you are seeing changes what you can see. The world's traditions have been doing this for thousands of years. You do not have to start from nothing.