The phrase "strong handshake" refers to the way someone grips and shakes hands with strength and firmness. It can signify confidence, assertiveness, and a reliable personality. Full definition
So, for a positive first impression, embracing social niceties — such as a good strong handshake — will stand you in good stead. (inspiringinterns.com)
Avoid an overly strong handshake or an assertive way of greeting. (abetterinterview.com)
However, liberal, intellectual women had stronger handshakes and made a better first impression than other women (Journal of Personality and Social Psychology, vol 79, p 110). (newscientist.com)