I hope, therefore, that this will be a useful guide to taking accurate measurements!
These are all the basic measurements you will need for sewing clothing:

So, let's run through them one at a time with tips on what you need to ensure for a perfect measurement.
First, if alone, stand with a straight back in front of a full length mirror. Use a sewing measuring tape that is soft. When reading the tape measure, don't bend over to see it, look in the mirror to read the number, while maintaining an erect posture.
But, for best results, find someone you trust, swear them to secrecy and then enlist their help!
1. Height
Stand erect with back near a wall, get friend to place a book on your head, with one end touching on the wall. Ensure book is level. Mark the lower edge of the book, measure from this to floor.
2. Bust
Wearing your best fitting, non-padded bra: Wrap the tape measure around the fullest point of your chest (normally in line with nipples), keeping the tape measure parallel to the floor. Ensure no fingers are included in the measurement, and that the tape is flat against the skin. Keep your arms at your sides. Breathe normally!!
3. Waist
Wearing only non-cinching underwear: Place the tape around the narrowest part of the waist - this is normally where your body creases when you bend side to side & forward. Keep the tape parallel to floor, keep it flat against the skin, don't include fingers in the measurement. Don't hold your breath, nor suck in your stomach. Stand erect and don't pull tape too tight, it should feel roughly like a pair of fitted trousers would if the waist band went around your natural waist. A good way to find your natural waistline is to tie a piece of ribbon around your waist (not too tight) and dance around. It will drop down to your natural waist. Measuring your waist daily, and the resultant dancing, may help reduce this figure :)
4. Hips
Wrap the tape measure around the fullest part of your hips and buttocks. Keep the tape parallel to the floor. Keep your legs together with your feet touching. !!Keep that piece of ribbon around your natural waist for further measurements!!
5. Back length
From most prominent bone at base of neck, along body to ribbon
6. Sleeve Length / more commonly ARM length
If a picture paints a thousand words, then how about a video?
7. Neck width - Neckline
This one is best done with a short chain or similarly weighted necklace placed around the neck, where it falls naturally will give you this measurement. The necklace should be short, but not a choker. It should fall just above your Suprasternal notch.
8. Side Leg / Outseam
From ribbon at waist along side of leg to desired length for trousers
9. Front waist length
Place tape measure at the top of your shoulder, at the base of your neck, and along the front of your body, over bust to ribbon. Dress length is from same starting point to desired length
10. Bust point
Measure from side of neck - same placement as for 9. along bust to nipple.
11. Upper arm circumference / Bicep
Measure around the widest point of your upper arm, keeping the arm in a upward right angle, but don't flex your muscles.