More. Granted I'm going off of my teens, early 20s and late 20s. I've found it to be something to work at.
Physically I have had the mixed fortunes of working a manual labor job for a couple years and have arms my current girlfriend's parents commented on. So be attractive; don't be unattractive. A little exercise goes far.
Mentally be sharp. I love video games but I have other passions. I built my own computer and my girlfriend was blown away as I had never done it before. I maintain my own truck that, "has been run into the ground" but still keeps on running courtesy of me.
Emotional maturity was super difficult in my opinion. To me it took learning from mistakes and what I really want in a partner. I would say the biggest is just not caring whether I'm with someone or not. Not to say I don't care about my girlfriend, I do quite a bit, but that when single I was ok with being single and was pursuing girls as I pleased instead of out of desperation.