Hello Lurch, don't worry... your English is perfectly clear.
The most efficient way to learn is to have the guidance of a good teacher. It is often difficult to recognize your own weaknesses, whether they be technical or musical understanding, because when you are playing, you are too busy doing other things to notice them. Having someone observe as you play and direct you to work on the biggest weakness that stands in your way is priceless.
There are some useful books on practicing that you might want to read.
On Practicing, by Ricardo Iznaola [ISBN 978-078665873-2]
The Art and Technique of Practice, by Richard Provost [ISBN 0-9627832-0-X]
In both of these books there is a distinction made between "playing" and "practicing".
Both recommend that you practice with a particular goal in mind, not just "I'm going to work on this new piece."
They tell how to create a practice schedule, keep a practice log, set realistic goals, etc.
Working with a teacher is helpful when you have tried everything you know to solve a problem, but none of those solutions have worked. Also, a good teacher will know when a piece is way beyond your abilities , and suggest another piece or etude that will help you build the skills you need to play the piece you really liked.
When the sun shines, bask.
Classical Guitar forever!