I know this sounds like cliche advice, but focus on your conversations. I have been on the other side of recruitment a couple times now, and most of the girls I talked to were cute but after talking to three girls over 11 to 12 parties, I don't even remember what half of them look like. I DO remember if I talked to a girl where I had a great conversation.
As for more solid advice, I agree with the above posters that you could pick out a statement piece of jewelry, or maybe as you said a cute headband each day! My fashion advice however has always been "if you have to ask if it looks good, you probably shouldn't wear it"; wear something that you will feel comfortable in and don't try a wild hairstyle/trend without seeing how it looks on you first. You can get a natural looking (SUNLESS) tan, look up what haircuts/styles are really popular for your face shape, and work out to both make yourself healthier but it will also make you happier.
Don't overly focus on your appearance though, because there are going to be prettier girls (there always is in every situation in life) and if you value your personal appearance over your personality, your going to shoot yourself in the foot before rounds with a drop in your self-esteem. Also, even if you talk to a supermodel sorority member, don't assume for any reason you aren't good enough for them.
At the end of the day, when I am recruiting girls I'm not looking to form a "hot girl posse". I'm recruiting girls that I can see myself becoming best friends with, if you are confident and sweet (but yes, at least polished too) you should be fine

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And to Loyally Kappa... While being presentable is important, people cannot control what they physically look like to an extent without plastic surgery. I hope that when you recruit girls you look for if they would fit in your chapters personality as well as if they match your nationals ideals.