Long title: How to get girls to stop worrying so much about how they look.
Let's assume that for an individual 'Z' we can graph the compatibility of some number of potential mates on a graph with two axes. The X axis represents physical compatibility, and Y axis well call mental compatibility though in truth it represents all qualities that are not physically visible, such as intelligence, humor, spirituality etc. Since this is all theoretical and not based on any actual measurements we can assume that compatibility is an absolute value, which is to say that the more compatible you are with someone, the happier you will be.
Now lets also assume that there is a minimum level of compatibility that you must have to maintain a successful marriage. Those in sectors 1, 3, and 4 are incompatible in some fashion and should not be pursued as a potential spouse. Whereas those in sector 2 are all good matches.
The way to maximize compatibility is to approach those in sector 2 in order of decreasing compatibility, based on some balance of the importance of the two axes. Here are two examples, one skewed towards mental qualities and one skewed towards physical qualities.
Before moving on let me restate that this is strictly addressing orders of approach. Also any person in sector 2 is someone our approacher, Z, would be happy with. Alright Here is the thing, humans are not psychic and have a limited capacity for looking at a person and knowing whether or not they would be mentally compatible. So we have to deal with the reality that all human patterns of approach are going to skew towards the physical, sometimes extremely so. This means that Z will be approaching people in sectors 2 and 4 equally.
Up until this point we've been talking about Z, and what would make Z happiest in a marriage. Now lets look for a moment at someone on the graph, who we'll call Q. Q knows Z and wants to date Z. If Q must wait for Z's approach then the best way for Q to speed up the process is to move up in the order of approach. Q must make itself more attractive to Z. If Q is already in sector 2, then the question is what is the best area for Q to focus on, mental or physical?
If Q improves mentally, then there is no advantage gained for a physically skewed approach by Z.
If Q improves physically, then a clear advantage is gained.
Now is also a good time to point out that if Q has to wait for Z to approach then Q is in 'competition' with the other people on the graph even if those people have no interest in Z. The only way for Q to move up in the order of approach is to be more attractive (esp physically) than the other people on the graph. Lastly, as I said before humans are not psychic and Q cannot know what Z will find more attractive, and so Q looks to popular culture, and other people to guess what Z might like.
Now lets talk about boys and girls, and how what I've been describing here influences the behavior of boys and girls. In our culture girls do not traditionally ask boys out. Which means that girls, more often than boys find themselves in Q's position. This causes girls, more than boys, to view other girls as competition, and to rate themselves against each other. It also means that, if a girl's goal is to have a relationship than the best use of her (finite) time is to have just enough mental qualities to be in sector 2, while being the most physically attractive girl around.
I believe that this is also what leads girls to obsess about what boys find attractive. Since girls don't actually know they have to guess, and are never certain and can never be comfortable that they've done enough. I also think, that since boys are so rarely in Q's position they are blissfully unaware of the dynamics at play here.
So what is my solution? Girls and Boys should feel equally free to approach each other romantically. Because in a society where girls must wait to be approached, while at the same time are told that marriage is a vital part of their lives and worth as a person then the best use of a girl's time is not in improving herself overall, but in focusing her attention on how she looks.
 I'd like to reiterate that these are compatibility ratings, and are subjective and personal. Which is to say that someone who may rank low on the physical or mental axis is not necessarily ugly, or stupid. They might be ugly or stupid, but it may just indicate incompatibility with the particular person on whom the graph is based.