I think that one of the first steps would be to review any directions or requirements of the particular project. In many creative projects like this one, the instructor will give some specific elements or rules that have to be followed. Prior to starting any creative endeavor, it might be good to make sure you know what has to be included.
Most shield projects revolve around the use of color, design in terms of graphics, and effective representation of who you are and what you believe. The shield or coat-of-arms project is going to require you to focus on elements like this. I think that one of the first starting points would be to ask what some essential elements to your identity are. For example, you might have to include a personal motto about yourself. What would be a phrase that would describe who you are or your belief system? That might be a good place to begin. Another element would be the use of color. All shields would have to have color elements to them and using colors as a way to accentuate character traits might be another element to focus on when you start your shield. The colors you use as a background and borders for your coat of arms can communicate much about you. It might help you tremendously to ensure that you have determined a color arrangement that can accentuate personal qualities. Finally, I think that you might need to determine which symbols you want to include on your shield that could convey what you want known about you. Animals or other symbols might be effective here. For example, shields with a lion can communicate a sense of power, while shields with birds on them can transmit ideas about surpassing borders and boundaries. Symbols, color arrangements, and mottos/language can serve as very good starting points in creating a shield or coat of arms about yourself.