The thing you always read about practicing is "It's better to practice 20 minutes a day instead of 4 hours once a week". What can I say? This is not only true for fingerstyle guitar.
But there is a difference between practicing and playing your repertoire (the pieces or songs you already master). You should definitely play your repertoire on a regular basis (I usually try to play my entire repertoire once a week, and this works well for me). Otherwise you will inevitably forget how to play your pieces.
The important point here is: Playing your repertoire is not practice. You won't make any progress if you only play the pieces you already master. To make progress, you need to learn new pieces and techniques in small steps over time. Learning to play the guitar is a long-term thing. In the end the small steps add up and lead to mastery of the pieces and techniques you practice.
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The most important rule when learning a new piece is to start as slow as possible. You can play any piece on this planet without prior practice if you just play slow enough.
Start with one or two bars and practice them until you can play them. Also try to memorize what you have learned. It will help you a lot if you are able to play your pieces by heart. If you can play the first bars, switch to the next ones. Do this until you have learned all the bars of the first verse or chorus. Then - also very slowly in the beginning - try to connect the practiced bars.
If you are always playing alone without a band, it's very easy to overlook timing problems, but eventually these problems will come back to you.
To avoid this, do yourself a favor and use a metronome when practicing. It's very annoying at first, but you will get used to it. If you can play a piece very well, you don't have to use a metronome every time, because you have internalized the timing of the piece.
The second thing about using a metronome is that most people tend to practice too fast. If you practice too fast, you need more time to really master a piece. So again, do yourself a favor and use a metronome. Even if you practice very slowly (e.g. 30 beats per minute), you should use a metronome.
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