Take your actual body measurements, as they are more accurate than measuring over your cloths.
Collar : Measure around neck base where the shirt fits.
Chest : Measure around fullest part of the chest. ensure that you place the tape close under the arms and make sure that the tape is flat across the back.
Sleeve : Measure from the collar, along the shoulders and down the outer arm to the hem.
Waist : Measure around the natural waistline.
Inside leg : Measure from top of the inside leg at the crotch till the ankle bone.
Outside leg : Measure from natural waistline to hem.
Centre back length : Measure from the center of the collar seam to the hem.
Note: This size chart is generalized, may vary country to country.