Aiming
Basically there are two ways of aiming - gap shooting/aiming (while looking along the arrow) and instinctive aiming/shooting. But there are some rules that have to be regarded with any way aiming.
1) Always aim and release the string with the string hand ay always the same anchor point. When you are trained enough, you will be able to hit from different weird positions (which is true especially for instinctive aiming). But at the beginning you don't have a chance to learn something if you will shoot always from a different position and the arrow will behave always in the different way.
2) It is important not to jerk with the string hand during release. With bad technique of release you will move the bow or arrow always in a different way, so the arrow will fly also always in a different way, regardless of aiming. Again - if you would jerk always in the same direction and same amount, you would be able to accustom to it. However the "jerk" is characteristic in that it is always different.
3) Do not aim long. It is because of fast shooting (if I want to whoot quickly, I must not aim for long), but also because of physical properties. The longer you hold the bow drawn, the more will your hands be fatigued. They will start to shake and bring bias to the shot. In the ideal situation you will shoot axactly in the time your string hand reaches the anchor point. You can do it mostly with instinctive aiming.
4) When releasing, it is neccessary to take care of position of arrow, that must touch the bow. If it will not, you will miss a lot. If you nock your arrow to the inside of the bow, it is helpful if you take it lightly with index finger of bow hand. If you nock to the outside, you can take it with thumb or index finger of the bow hand.
5) The position of arrow on string is also important - arrow must go horizontally, not up or down. But this is what you cannot influence during aiming, it must be ensured when nocking.
... probably many more potential mistakes could be found, but it is not neccessary to describe them. There is one general rule - if you move always the same, it is not mistake. Mistake is everything that brings randomness and chaos to the shot.
In following text I write about instinctive and gap aiming. In reality both techniques blend. Gap shooters after some training start to rely on instinct partially, because when drawing the string they already "know" where it will fly. On the other hand instinctive archer may get to the situation where for example he realizes that he has heavier arrow than usual, so he consciously aims a bit higher to compensate it.
The difference between the two techniques on the level of psychology could be described as this. Instinctive archer concentrates on where he wants the arrow to land, and relies on his brain to subconsciously take care of all details neccessary for such result. Gap archer concentrates on each little detail of the shot, and relies on that if all of them will be correct, then the arrow will land where he wants to.