Smile! I don't say that anymore. Trying to get someone to smile when they don't really want to or just being in front of a camera can make their smile look forced. Spending a little time with the person and talking about anything (but the photograph) as you begin the session you will usually find they relax and you get real smiles.
I had a nice visit with my friend Sarah today. We hadn't seen each other in some time so spent a few hours catching up. We started outside the coffee shop but it clouded over so we went to a table inside which just happened to be right by the window. So naturally the camera came out for a little bit.
For some people their smile is so easy and natural it lights up right into their eyes and it's, brilliant.
I used the 24-70 2.8 at 60mm 1/125 sec f3.5 iso 100