Does there exist some kind of "wrong" practice?
Only most of the time, by most people. It's one of the reasons they can't progress. The other is that they don't want to.
And what does happen when your practice is "wrong"?
First thing - you don't know you're practicing wrong. Second you get tired, bored, frustrated and angry.
What do you think of the often heard "Just throw your darts"?
I use the same phrase. Once a person has reached the point where their mechanics are as sound as they can be, or want them to be, then 'just throw the darts' or as Jeff suggests: 'just play the game.'
Should you observe and analyse your throw in practice or would you say do it as in competition and feel only interested in the result?
You should never think while on a competitive oche. Thinking is bad for a dart shooter. It's what a dart player does. Think during solitary physical practice - only.
Should you keep notes of your practice results? And how much do you learn from practice results or achievements about your skills in competition?
Beamen set a personal best at the Olympics in Mexico. He jumped two feet beyond the world's record. If a person tracts their practice results they will most likely end up competing against themselves which would be like Beamen using his jump to gauge how well he is doing in practice. Never, ever, never, ever compete against yourself. I've tried not to be ambiguous here.
One very important point for you is that good practice is not quantity, but quality. What would you say makes a quality practice?
You leave the board with a sense of accomplishment.
Do you think in future there'll be real darts coaches like coaches in other sports?
No I don't think so. Back to my basic concept. A person has to learn for themselves and will be ready for new techniques or concepts when the spirit moves them. Trying to coach someone who has not learned and accepted the techniques a coach wants to use is not only not helpful, it is damaging.