Experience and knowledge. you can't rush that ;-)
Ok, so first you need a reference point. A headphone or speaker system that has a bass texture, punch, kick, attack, speed, impact (add more adjectives to describe bass here) that you like. Then listen for that particular part on a set of different headphones. How does this headphone render this particular bass part in a specific song you know inside out. Do you hear all the nuances that you know are there? Do you hear more, bloated, or less and thin bass?
I would recommend to read a small guide to "critical listening", just search here in this forum or on google for articles about it. However, in general, you should listen to the music and loose yourself in the music rather than listening for artifacts and technicalities of the medium you are listening with. But for finding out some specific qualities of a headphone, it's good to take back on enjoyment and listen to details.
Hope that helps,
Edited by Koolpep - 4/27/14 at 11:11pm