It is very difficult to grab a good candid portrait of someone. The process of creating a good photographic portrait involves visual composition and posing. One of the fine details in posing are the hands. Placement of the hands and each finger can put the icing on the cake.
|Source:Doug Box's Guide to Posing for Portrait Photographers|
I recommend visiting a site with a lesson on hand posing, an excerpt from the book Doug Box's Guide to Posing for Portrait Photographers provided courtesy of Amherst Media.
Learning to pose will increase the quality of you images.