If you want to measure your body, always use a cloth measuring tape. If you want more accurate results the best thing you can do is to have a partner to measure you. Also if you want your measurements for fashion, using a cloth measuring tape is important because the clothes are also measured from that measuring tape.
Remember to wear proper undergarments that you generally use. For example, if you wear a special support bra take your measurements with that bra on.
We highly recommend measuring a properly fitted garment and comparing those measurements to the ones you take.
Shoulder Width:
Measure across the back from the corner of one shoulder to the corner of the other shoulder. For this measurement, I recommend measuring a jacket you already have that fits properly. Laying the jacket flat, measure from shoulder seam to shoulder seam.
Bust:
Measure around the fullest part of the bust. This measurement is taken above the band of your bra, and may not be the same as your bra size.
Waist:
Measure the smallest part of the waist. The natural waist is below the rib cage and usually above the belly button. Do not take this measurement around the waistband of your clothing.
Hip:
The hip measurement is taken at the widest part of the hips. Do not take this measurement around the waistband of your clothing, or where your hands fall when you "put your hands on your hips."
Sleeve:
With one arm down at a slight angle, start from the corner of the shoulder and measure down to where you'd like your sleeve to end. You can also use a shirt that already fits you well. Just lay it flat and measure from the corner shoulder seam to the end of the cuff.