Have a goal each time you sit down to practice, measure your work in terms of completed tasks rather than length of time.Avoid brute force repetition in hopes that mindless repetition will automatically solve everything. Set a timetable to work from, don't just practice whenever you feel like it, write it into your daily plan, organize your time.Have an overall view of works you have studied, are studying and will study. Not knowing what to play next or where you are going can make you feel like you are floundering about just playing random music, motivate yourself with the work.Play for someone, if you just play for yourself all the time there is no pressure to improve.
Excellent advice, all of it. Thank you.
The bit about having a timetable, I'd say is something everyone should evaluate for their own temperament/needs.
...So it is a rather loaded bit of advice because it is implying that you need to improve your practice craft and you generally need a good teacher for this.
It is such an important issue that if I catch my younger students lie about practicing I will tell them, you don't have to convince me that you practiced, you must be honest to yourself because you know what is the truth. Too many live in fantasy or in what they can make others believe, they are not truthful to themselves, this limits progress a huge amount.