I have heard that you should always stand in the centre of the oche (even of you aim at the left or right side of the dartboard). Why is this? Is it bad to change the stance just to aim at the left side of the dartboard? Stephen Bunting always stand at the right side of the oche (and never change when aim at a special place of the board).
I have also heard that you're just supposed to aim for, eg treble 20, and throw the darts. Doesn't becoming a master of darts requier taking lessons from a pro?
I discuss standing and throwing with my fellow darts players, some pretty good shooters although none are pros, others with various skills, all the time and occasionally learn something that improves my game. I don't see how you could lose by taking lessons from a pro.
Regarding standing at the center of the oche, there may be more to that question than meets the eye.
First, standing at the center, you have the shortest possible distance from your hand to the center of the dartboard. But shooting towards one side or the other you will have slightly longer distances which you must accommodate with your throw.
You can move to the left or right to try to achieve the shortest possible distance, or the most consistent distance, when shooting at one side or the other of the board, but its very difficult to line yourself up exactly for every point you may need to hit on the board.
You can see from watching televised matches that the standing points of professional players vary considerably and few seem to be trying to find the shortest possible distance to the board.
When I throw, I line up with the center of the board and rotate my body, attempting achieve pretty much the same arm motion for every point on the board. Watching televised tournaments involving players that shoot much better than I do, I can see that some players use a similar method and some do not. But all seem to be very consistent in the throw that they do use.
My conclusion is that standing point, angle of body to the face of the board, arm motion and throw are very personal. The player through daily practice and experiment must find the most comfortable and successful personal throw, practice as frequently as possible to achieve a uniform throw which varies in small details depending on the location of the target on the dartboard.