Hit a lick means to commit an act that's considered a quick way to get money. For example robbing someone is considered 'hitting a lick', because it's done in an instant. The term originates from someone taking a lick of something such as a lollipop, it's quick and you essentially get some of it. The term is heavily used to refer to robbing someone such as a drug supplier or connect.
Hit a lick has been used by numerous rappers in their rap songs, for instance, in Yo Gotti's 'Cold Blood' song, J Cole says "See, I seen just what that fast money gon’ come and do to people - Hit a lick, it was a hit". In YG's 'Thank God' song, RJ says ""He hit a lick with his homies, his homies switched it on him. - They spent the money, he got greedy and put the pistol on him". In Gucci Mane's "Hit Another Lick" song, he says "New face 20's (yeah) - Damn Gucci Mane just took my money (yeah) - I sell alotta pies - I robbed a couple guys (yeah) - I'm stuntin' like a b*tch cuz I hit another lick (yeah)". In Lil B's "Finna Hit A Lick" song, he says "Yes, I'm finna hit a lick, yeah, I'm finna rob a b*tch".