This should be an obvious one, but we'll spell it out for you anyway; men are more attracted to women who take good care of themselves. And we're not just talking about showering every day and washing your hair, we're talking whole lifestyles.
It's a fact that sometimes when we're single, we go to the gym, work out, diet, eat healthily and do everything we can to make ourselves the most attractive 'me' we can be. But then as soon as we enter a relationship, we give up on all of that because we're happy, and we're no longer striving to attract new partners. Men aren't stupid, they notice this. If you're prepared to go to all that effort to make yourself beautiful, you should maintain it. Stay in shape, dress up for dates, and be the person you were when he met you for as long as you can. We all grow old but do it gracefully!