If the goal is to acquire a skill, it's about deliberate practice... I have to come up with a project I want to do, make sure I have energy for it, set time aside for some days, and take a step forward each day (or each other day..)

If the goal is to acquire new knowledge and explore new fields, setting 1h aside each day to read (and study/highlight) non-fiction books works very well for me. I am very strict about this, almost like a second job. For me, it's about acquiring and digesting knowledge gradually. More than 1h a day does not work for me.

Hope this helps!