People come in many shapes and sizes but learn how to dress for yourself and not for what you want to be.
Read that again, understand that, and be yourself.
I absolutely hate seeing girls who dress for the size they wish they were. There is nothing sexier than confidence. By trying to make yourself something that you're not, you look like you have absolutely no confidence. So the first step to dressing confidently is understanding your shape and realizing you are not the only one.
There are four basic body shapes:
Apple: You have broad shoulders, narrow hips, and your chest and stomach look larger compared to the rest of your body. Again, your top half is bigger than your bottom half, so ladies with an "inverted triangle" shape are included in this category for me.
Pear: You have slim shoulders, small bust/stomach, and wide hips/thighs.
Hourglass: Your hips and bust are almost equal and you have a narrow waist.
Rectangular: Your waist is not much smaller than your hips and bust. There are many names for this body shape (athletic is what it's usually called) but I've heard people say banana, straight, pencil, etc.
Well that was my little input for the day! I hope this helps every woman understand her body shape.