I learned to make pho from eating it, talking to good cooks and reading lots of cookbooks. Over the years, it's clear that there's no definitive way to do it. Each cook expresses his or her personal flair in a bowl of pho beef noodle soup. Along with Basic Pho Secrets and Techniques, I've added some more for your consideration:
Toast the spices. Though I don't think this makes a huge difference because the broth cooks for so long, some cooks toast the spices before adding them to the broth. For this approach, use a skillet set over a medium-low flame. Once the star anise, cloves and cinnamon are fragrant, remove them from the heat. Lightly crush the spices using the flat side of a knife or mortar and pestle. Encase them in cheesecloth or a mesh spice/herb ball and add to the broth.