A lot of it depends on your body shape in particular. Like my best friend, she's a little chubby, and not the most curvacious. What she has found that works for her are shirts with empire waists. This is where they are cinched or have a band/belt right below the bust in order to accentuate the narrowest part of her torso.
Now if you're more naturally curvy, you can get away with a lot (Except for empire waists ironically enough), and have more freedom to play with your clothing.
Necklines are always an interesting yet overlooked thing. Using my friend as an example again, she recently discovered cowl neck shirts and sweaters. This is where there is extra material around the neck that is either folded or hangs down.
The biggest mistake I see is too many girls trying to hide themselves. Baggy cloths can very easily look frumpy. But in contrast, clothing that's too tight can make a girl look a size or two bigger than what they really are (This goes for girls of ANY shape or size). So always try thing on first to see if they fit comfortably without too much puckering, stretching, or too much hanging off of you.
Here are a few examples I pulled off of google really quick:
Empire Waist:
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[A little big for the image itself here...]Just plain pretty:
[Too big to post picture]Cowl Neck Sweaters:
![User Image - Blocked by "Display Image" Settings. Click to show. User Image - Blocked by "Display Image" Settings. Click to show.](https://graphics.gaiaonline.com/images/s.gif)
[Again a little big to post the image...]The goal of dressing nicely is to feel confident in yourself. : ) It's all for you, not to show off for others. Find what you like and what you feel fits you.