Take off anything you will not be wearing under the garment(s) you are tailoring.
Put on any undergarments, blouses or other articles of clothing that you will be wearing with the outfit or garment you are tailoring.
Measure the hem length of pants, dresses or skirts by turning the bottom of the garment either up or under the desired number of inches and marking the place.
Or, use a previously hemmed garment if it is the exact length you want the garment you will be tailoring to be. Simply match the waistband or top of the two garments exactly and evenly, then mark where the hem of the already tailored garment lies on the other garment.
Use pins or other marking methods to show where else besides the hem the garment needs tailoring. Mark garments that need to be made smaller so you can tell how much material needs to be removed or stitched up. Mark garments that need to be made larger so where you can tell where to re-sew the garment after the original stitches have been removed.
Use a needle and thread that matches the garment to hand-sew hems or perform small tailoring tasks. Use the sewing machine to perform larger tailoring tasks.