First of all, start by tracing piece n°1, the front top, in the size corresponding to your bust measurement (here, a size 38). Then, trace piece n°3 (front bottom) in the size corresponding to your waist measurement (here, a size 40). For piece n°1, trace the notch corresponding to your bust size.
Now take piece n°2 (front middle). We’ll trace a line on the side of the piece (between the armhole and the waist) joining your bust and waist sizes (here, 38 and 40).
Join these two points using a ruler, as illlustrated above. Trace your piece using this line, and then following the line corresponding to your bust measurement for the top of the piece, and to your waist measurement for the bottom of the piece. As for piece n°1, mark the notch corresponding to your bust measurement (here, 38).
The principle is the same for the back bodice, if not easier. Join, as you did before, your bust and waist size on the side of the piece. for the strap marks, use those corresponding to your bust measurements.