Apply the same principle of the Personality Matching Technique to handshakes. Don't get confused by the "too hard" or "too soft" handshake psychology baloney. There is no absolute when it comes to handshakes because the effectiveness of the handshake is defined by the recipient. So is the handshake unimportant? No, it's very important, since it is often the first impression you provide to an interviewer. But it would be wrong to attempt to come up with "the perfect handshake" in advance. There is no such thing, since each person receiving your handshake has their own personal view of what is best in terms of a handshake. It's relative to the person who has your fingers within their grasp. Therefore, a truly effective handshake is going to be a "mirror" of the handshake being offered. Do your best to attempt to match the person's handshake the same as you would attempt to match their speaking cadence and posture.
While personality matching is dynamic and takes place over an extended period of time, the handshake lasts just one to two seconds. So how do you adjust? Start with a medium-grip handshake, placing your hand so that the soft skin between your thumb and forefinger comes in contact with the same location on the recipient's hand. Then be prepared to squeeze down on the gorilla or lighten up on the softie, as necessary. Don't get into a wrestling contest. Again, just as in personality matching, you don't have to match the extremes. Just move to that end of your "handshake range." Practice a few times with a friend. Or better yet, practice with a loved one.