Something that separates a decent photo from a memorable photo is capturing your subject's personality. If your client is nervous or unsure, achieving such a feat can prove difficult. James Brandon over at Digital Photography School offers some tips to easy these situations.
One of my favorites:
If I’m photographing an engaged couple, things can get pretty steamy between the two....When I tell them to kiss while I take a few shots, sometimes I’ll say something to the effect of “Whoa there, let’s pull it back a litte, I didn’t say make out!”
The usual result is a light hearted laugh and a fun, almost candid photo. If you would like to see the rest of the tips that James Brandon provides, you can find the article here: Your Best Lines To Make Clients Laugh or Act Natural