Factors to consider while buying beginner audiophile headphones:
Clarity/Transparency - Does the headphone sound pristine, or is there some muddiness to the sound? Can you pick out and hone in on individual instruments? Does the bass "stay in its lane", or does it sound like it spills into the low midrange?
Comfort - Long, leisurely listening sessions demand a headphone that won't be a distraction to your head. Now, comfort is subjective - what fits one person properly, might feel too "clampy" on another person
Soundstage - This refers to the sense of space that you perceive when listening to your headphone. When you close your eyes, can you easily envision the various instruments and vocalists spread out on a stage in your mind's eye?
Design - Headphones are made with an Open Back or Closed Back design, and both offer a unique sound. Closed backs keep the sound in the headphones, preventing that noise bleed that makes public commutes and studying in the library painfully awkward. Open-back headphones do not attempt to keep the noise in, the speaker emits sound into your ears and out the backs of the headphones.
Tuning - Tuning has to do with how audio frequencies are presented. Tuning is related to the sound signature, as the way a headphone is tuned will contribute to its sound. On a headphone with neutral tuning, no single frequency will be emphasised. Other headphones are tuned to boost in the bass or the bass and treble or the midrange.