Let me start this post out with a disclaimer: I believe 100% that you should wear what makes you feel good. I wear all kinds of things that are not "ideal for my body type," because it is my general belief that being comfortable and confident are much more important than perfectly balanced proportions.
That being said, there are important times when knowing what flatters you most will be very important, for instance, when you're shopping for jeans, a new swimsuit, or your wedding dress. Also, when you're doing anything that involves a lot of photographs of yourself, you'll probably like the end result much more if you're in something that is as figure-flattering as possible.
So the point here is not to steer anyone away from things they want to wear, but to simply give you the tools to make the best decisions when shopping for these things. But first things first, you can't dress for your body type unless you know which body type you actually are! This might seem simple, and for some people/bodies it will be, but if you fall in any sort of gray area (I actually was reading myself incorrectly for years), it's worth finding out for sure.
First, you'll need to take your measurements...
What you need:
calculator (and math skills/patience)
possibly a friend for help/moral support
What you measure:
Shoulder: This one is a little tricky to do on your own. You want to measure the largest circumference of your shoulders. Place the measuring tape at the tip of one shoulder and wrap it around you so that it skims your shoulders loosely like a shawl.
Bust: With your posture straight, wrap the measuring tape around your back (like where your bra strap sits) and over the fullest part of your breasts (usually the middle). Pull the tape as tight as it will go before squishing your breasts.
Waist: Wrap the measuring tape around the smallest part of your waist. If you have an undefined waist, bend side to side, and the axis of the bend (the part that folds inward) is your waist. The measuring tape should go around your back and end near but above your belly button.
Hip: Hold the measuring tape below one hip bone, at the fullest part of your hip (usually around 7-9 inches from your natural waist). Wrap it around the largest part of your butt and back around to meet at the front.
If you need more help finding measurements, this WikiHow article has more info and helpful graphics.
So you have your measurements, now it's time to find out your body type. This is determined by ratios, your hip measurement as compared to your waist measurement, for example.
I'm focusing on four shapes: hourglass, triangle, inverted triangle, and rectangle. Though there might be some other variances in shape, these four will cover most body types. To start, choose the one (or two) that you think will most likely be your shape, and then check the math with your measurements.
(Sidenote: To find 5% or 25% of a number, just mulitply by .05 or .25, respectively. So for instance, on the hourglass, with a hip measurement of 35, you would need to determine 5% of 35 (.05 x 35) which is 1.75. So then, the shoulder measurement would need to be between 33.25 (35 - 1.75) and 35 inches to classify as this bodytype.)
Now that you know you're body type, stay tuned for specfic styling tips on how to best work what you've got!
If you have any questions or find anything confusing, please let me know in the comments and I'll try my best to help! :)