How do I know if I have poor blood flow (in feet)?

Get an exam. The best way is to be evaluated by a podiatrist. They can do a complete exam and decide if you need to be sent for further testing. If your feet are cold or you have trouble healing wounds you may have decreased blood flow.
Pulses. Check for pulses on the top of the midfoot in line with the second toes. Also on the inside, big toe side, of the ankles. Poor ciculation could also create a pinkish redish color when your feet are down. Pain could also be a symptom.