1. A person who can ease their way through things, typically using words. Also may be a player
. It seems this person may have a way with words and always knows what to say.
2. They may also be cunning, wily, and might be willing to lie, cheat, or steal to get what they want.
You can refer to the song "Smooth Operator" by Sade, read the lyrics, and it may help you.
It has good and bad connotation, it all depends on how it's used.
1. Dang, that girl don't look it, but she is one smooth operator. She just got a date after a five minute conversation with him.
2. That man is a smooth operator, he just dumped a girl and has a date with two new ones.