Find a T-shirt that is long enough to be a dress. Try your T-shirt on inside out. Make a mark where you want your dress to cling to your body. This could be at your waist or under your bust. Take the T-shirt off. Draw a horizontal line with chalk all the way around it at the level you made the mark.
Mark the middle point of this elastic by folding it in half and putting in a pin at the fold.
Position your elastic over the line you marked on your T-shirt. Put the sewing machine foot - and needle - down on top of them. With your right hand, gently pull the elastic towards you so the pin reaches the side seam of your T-shirt. This ensures you sew exactly half of your elastic onto each side of your t-shirt, so your folds will fall evenly.
You can leave this edge ‘raw,’ as T-shirt fabric will not come unravelled, or you can use bias binding to create a professional decorative finish. Bias binding is like ribbon made of a stiffish fabric. The strip of fabric is cut ‘on the bias’, which means the fibres run diagonally through it, instead of vertically and horizontally. This gives it flexibility to bend.
You need a piece of bias binding that is slightly longer than the full distance around the neck line. Fold the bias binding in half between your thumb and two fingers, and poisition so that it encases the edge of your fabric. Sew it down with straight stitch, catching both the front and back of your bias binding, with your fabric sandwiched in between.