Earlier I talked about the 50mm F1.4 "prime" lens and its use. One of the things its best for is portraits. Its narrow depth of field means you do have to step back a bit, but it does a great job in low light and focuses quickly.
I prefer taking people pictures when they don't know they're being photographed. You can never say, "act natural" and expect that to happen. People might get annoyed, but the pictures are more candid and natural.