Taking someone's portrait is one of the hardest things for me. The most tricky part for me is to actually go to that person and tell him i'm a photographer and ask his permission for the photo. The next challenge is to wait for him to stop posing and start acting natural. That part might take some time and requires some patience. The last part and maybe the one that requires the most thinking is to understand what is the best way to capture the person's personality in a single frame. In most times, I try to imagine the final frame before even approaching him/her, simply so I won't waste their time by staring and thinking.
I learned that talking to the person while getting them comfortable is great in getting to know the person, hear some interesting stories and building some trust