What you asked is self explanatory. You can monitor your DHT levels, and of course the more 5 alpha reductase type II inhibitor you take, the lesser DHT levels you'll probably show.
If your family has Male (your mother doesn't count, only your mother's father) Pattern Baldness history then you will need a DHT inhibitor.
Low testosterone levels also work. My grandfather was Norwood 7 and beyond, my uncles are all Norwood 7, but my father, who has been an athlete throughout his whole life, is a Norwood 4. Physical exercise(marathons and long lasting aerobic exercise) has been proven to reduce testosterone levels, which helps to produce less DHT, which eases the disruption of DHT sensitive hair follicles, which reduces hair loss.