Students often complain about foreshortening so I now reveal Secrets of Foreshortening
1 - look closely when you recognize a foreshortened situation - and all interesting poses have them.
2 - see what form is overlapping what form
3 - sketch a light blocking in or gesture of the pose including the foreshortening. See Chapter 2 in the Basic Figure Drawing Techniques textbook (BFDT)
4 - look again at the foreshortened sections and measure (See Chapter 3 in BFDT)
5 - sketch in your measures on top of your gesture
6 - use eraser and darker drawing medium to reconcile the gesture with the measured adjustments
7 - look again for overlapping shapes and refine the shape with lots of very focused seeing of overlap and measuring.
8 - keep reconciling what you see with what you draw by continuing to refine.
Step back often and refer to both your drawing and your model.
Yes, it's fun - like a puzzle - putting all the right sized shapes together will equal a realistic picture.
Image Source: http://gekos.no/art/index.php/pdf/the-practice-and-science-of-drawing.pdf