David Allen, Getting Things Done:

<https://en.wikipedia.org/wiki/Getting_Things_Done>

<https://gettingthingsdone.com/>

Start with the book.

The concept is something of a perennial favourite with HN: <https://hn.algolia.com/?q=%22getting+things+done%22>

A mentor, coach, therapist, or partner can help as well.

You might want to check for underlying issues such as ADHD, though ultimately you've still simply got to establish goals, make a plan, and execute on it.