This whole text is a TL;DR. I hope you’ll be able to use it as a reference if and when things get really confusing for you.
This is a shortlist of the most useful approaches to practice I’ve come across in 20 years of playing, practicing, reading and thinking about music of all sorts. I will constantly update this as I remember and discover practice tactics. This isn’t a place for style-specific approaches; you can Google for that. These are broad principles that help musicians in every style on every instrument free themselves to truly play.
Where I can, I’ve included links to videos that illustrate these concepts with clarity and brevity. If you’re short on time, 1.5x speed the video.
Yoda was right. “Trying” to do something is useless. Either you can do it, or you can’t. If you can’t, generally you’ll become able to if you do lots of things like it.
A corollary: thinking and doing are different things. Think about doing someth
Be specific. Don’t tell me (or yourself) that you played “well” or “badly” when you’re practicing. Look for specific changes that could be made, and make them. Don’t worry about whether you are good or bad, because it’s irrelevant- your intonation can be improved, your time can be improved, your sound can improve, but you are just you, and there is no useful, reasonable way of judging the whole musician or person that is you as good or bad.
Your voice is your direct line of contact with your musical concept. Strong singing opens the possibility of strong playing. By strong singing, I mean singing with purpose, with personality. It does help if you’re in tune and if your tone is pure, but those are secondary considerations unless you are primarily a singer. What matters most is rhythm and concept. If those are good with your voice, you can move to the instrument. If they’re not in your singing, it is not at all likely that you will be able to play well because you do not have a clear enough concept of what you’re trying to do to sing.
Get it with your voice, and the instrument will follow.
You learn better if you space out study/practice sessions. 20 minutes a day is better than 140 minutes once a week, and 5 minutes of scales at the beginning, 5 minutes of playig, then another 5 minutes of scales is generally better than 10 straight minutes of scales (assuming only 20 minutes to practice).
This one’s simple. You’re probably going too fast most of the time. Even if you think you’ve got it on lock, slowing WAY down once in a while can show you incredible things about your playing, and it’s never a bad way to start with something difficult. I’m talking quarter notes or even eighth notes at less than 50 BPM on the metronome.
Zoom in, zoom out
Zoom in on a problem area, even if it’s all the way to one or two notes. As you improve it, mix in practice with all the surrounding notes, start in various places in the scale or passage, and make sure that you can execute your solution in context. This one gets tons of people, even plenty of college students. Don’t be a victim to practicing out of context.
Variation/vocabulary of ideas and movement
“Blessed are the flexible, for they will not get bent out of shape.”
You’re not a machine, and you’re never going to do something exactly the same way twice. In fact, there are a number of ways in which the body can move to accomplish any given goal, a whole range of possibly “correct” solutions to any musical puzzle.
Practice your material at a variety of speeds with a variety of different articulation, phrasing, etc. Start in different places all the time- you should be able to play easily from anywhere. Don’t make yourself stiff by becoming overly reliant on specific conditions being fulfilled to succeed- the more different ways you practice, the easier it is to sail through “mistakes” and give consistently good performances.
This will also allay the possibility of repetitive strain injuries.
If you need to play something fast, this is a brilliant way to get it there.
Mental practice is your best friend
It’s all in the name- you can make incredible progress with any skill, musical or otherwise, by going over it carefully in your head, visualizing the sounds, sights, and feelings of successful performance as clearly as you can.
There are plenty of theories about how and why this works, but just know this- it does. There are dozens of anecdotes and studies to recommend this mode of learning, and if you need more evidence, just try it yourself and notice the improvements you make.