Stamina is the biggest criterion. You need to be able to fuck a woman however she needs so that she gets off repeatedly (before you get off once) so that she comes to rely on you for her sexual pleasure. The whole big dick, muscular thing is really more from porn than real life. Some women like to be made love to, some like to be fucked, some like to fuck you. Some want a huge cock, some can't handle anything over 5 or 6 inches for longer than 5 minutes though. Some want their husband there, some want to be discrete.
What every hotwife I've met have in common is hubs can't get them to a g-spot orgasm (much less several in a row). There's often some other kinks--voyeurism, exhibitionism, big dick, younger man or older--but the common denominator of what they're looking for is they want to be fucked for longer than what they're used to.
So work on the stamina.