Good looks are nice but substance is more important. If someone is a good person they will look beautiful when you you get to know them where as if someone is good looking but has a bad personality they will not be attractive.
Looks are only a little bit of how attractive someone is for me: I think that the way someone behaves, talks and acts is also really important. If someone is kind, funny and charasmatic they can be attractive no matter what they look like. Ultimately, I think most people are looking for someone they enjoy spending time with.
I know a girl who finally went out with a guy she had fancied for ages: she thought he was really nice and as a bonus he was also good looking and had a great body because he worked out loads to impress girls. However, she dumped him in less than a month because he just spent all his time at the gym so he would look good and no time with her, which shows that, although working out loads might impress girls initially, its not going to keep them interested. I think being fit and healthy is great, but its not the most important thing in attracting a partner, and certainly not the most important thing in keeping them.