Here's a quick trick to help you out, courtesy of researchers at the University of Illinois.

They discovered that when 2 people meet, the person who extends their hand for a handshake FIRST leaves a better first impression.

The researchers actually monitored brain scans as people met, to see how the brain reacted to different parts of a first meeting.  Nothing was more tied to a positive first impression like extending your hand first for the handshake!

But, it's also important to give a GOOD handshake.  They found that you could waste a lot of the goodwill from initiating a handshake if yours is limp or weak.

No word as to what happens when you extend for a high-five and are left hanging...

Source: Doctor Tipster