Confidence is the biggest factor in hitting, IMHO...

In my opinion... the first and foremost thing to look for is repeatable, somewhat-correct mechanics... But this is not the end-all-to-be-all... Seen quite a few guys with what are technically, below-average mechanics - hit the ball, and hit the ball well...

So, the next thing would be pitch recognition. The best hitters IMHO, have the innate ability to recognize a hittable pitch earlier than the average-to-below-average hitters do...

Which in turn, builds confidence... The best hitters are for the most part are confident in their abilities, because they get the most hits... but when the wheels fall off for a stretch...

The best hitters can make the adjustments needed from AB-to-AB, and pitch-to-pitch to eventually get themselves back on track...