I had to spend some time in a mall this past week because that is where the Lenscrafters was where I had to go to get my glasses fixed. The worst "trend" I saw was girls wearing their clothes way too tight.
I think the #1 thing I would like to see is for more girls to understand their clothing size is NOT the tiniest garment they can cram their bodies into. Wearing ease, people. Learn it, wear it, love it. Nothing looks more painful than a size 5 girl packed into a size 1 pair of shorts. Body bulging, seams straining, this is not the look to buy.
If you have had a growth spurt or hit your Freshman 15, please, go up a size. If you are just being tag conscious, get a grip. There is no shame in wearing a size 9 if you really are a size 9, and you will look much more graceful and attractive if your clothes aren't gapping and bunching and straining around your form.
If you think you should wear a smaller size, work out more and take care to eat healthy, and buy your preferred size when you can fit it. In the meantime, wear clothes that fit your body the way it is.
That's all.