So why do you want to do X ?
Suppose X is learning Spanish. So you might say you want to travel, or translate Neruda. If you don't know why you want to learn Spanish, then think about it for a moment. You can travel with very minimal Spanish. Becoming a Spanish professor is something more than that. You can translate with imperfections in your knowledge. There are many gradations in between.
The next question, then, is what your goal is. It can't be "improving my Spanish," because that is imprecise. It would have to be something very exact. For example, I want to be able to play jazz piano with a certain competence level. I need to break this goal down, and figure out what specific aspects I need to work on.
Now you have to identify very specific weaknesses and work on those. A lot of your effort must be directed toward the weaknesses.
For my piano playing, I can identify strengths:
1. I have good understanding of theory and can compose tunes. I can read & write music ok.
2. I am motivated. My retirement plan is to be full time composer.
3. I have listened to enough jazz so I recognize many, many tunes.
1. Everything else. More specifically, I am not a technically accomplished player.
2. I need to work a lot with the metronome and solidify my time.
3. My playing doesn't sound jazzy enough. It is too stiff.
4. I am not good at improv.
5. Same for comping.
6. My ear can always stand improvement.
So my new year's goal for piano are:
1. Record again at the studio.
2. Learn more chord extensions: 9th, 11th. 13th.
3. Have a more fluid style.
4. Give a recital.