to follow suit is to do the same
as the previous person did. So if your entire sentence is something like "The dollar is falling, and the market looks poised to follow suit" it means the market appears to be about to fall, too. (The expression comes from card games of the Whist family, in which "follow suit" means to play a card of the same suit (spades, hearts, diamonds, or clubs) as the person who started the round.)