They say practise makes perfect. Well, not so much. Sloppy practise doesn’t do anything but reinforce bad habits.
There is a tendency to work on a new piece by just going through from beginning to end. This means the sections that have been mastered are practised just as much as those that have not. Rather mark the trouble spots and concentrate on them. It also doesn’t help to get the awkward spot wrong five times, get it right once and then stop. What your brain and fingers will remember is the five wrong times. Try to get it right at least three times in succession.
There is a huge tendency, particularly with beginners, to try to play faster than they are able. Speed will come, but if timing and accuracy are ignored, the same mistakes will only be made faster.
It is far better to practise regularly at least 5 days a week, rather than trying to catch up the day before. If the guitar hasn’t been touched in a week, chances are excellent that most of the lesson has been forgotten. Little and often works better for another reason as well – it is difficult to focus well for long periods of time. Surprising progress can be made with short, regular sessions.
It is also not practise to run through all the old pieces that have already been mastered. It’s fun, but not all that productive.
Technique is the best way to do something, not the easiest or most comfortable. Just because a simple piece can be played with faulty hand positions doesn’t mean that it will work with more advanced pieces. And having to get rid of bad habits takes far more time than doing it correctly in the first place.
If you are not working with a teacher, it is up to you listen to yourself critically. Record yourself if at all possible. It is even better if someone can take a video of a practise session. Keep them to look back on occasionally. It can be very helpful for those times when you seem to be standing still.
Technique never stands still, it is either going forward or backwards. If you’re not challenging yourself and playing regularly…