I've learned two most important principals. However, the first precept was not so much learned as it was already an adopted axiom.
First and foremost, ALWAYS trust your ears! It matters not what others' ears prefer or like. YOU are the one who needs to be pleased or impressed and live with the decison(s) you make.
Lastly, in order to achieve, not just a small, immediately discernible improvement in sound quality but that proverbial wow factor, the expense is exponential. In other words, GENERALLY SPEAKING, two-thousand-dollar speakers will sound better than one-thousand-dollar speakers. However, if you want that wow factor, plan on spending at least three times as much and, from there, the exponents increase for the wow factor.