First: accept that this will sometimes happen on the social dance floor with a not-so-experienced leader OR one who is working on a newly-learned move.
Importantly, be gracious and be diplomatic. Followers are taught to follow a lead without conscious thought and, when a lead is not clear, it is entirely possibly that the move that a follower dances is not what the leader intended.
One suggestion is to discreetly apologize to the leader and ask him/her to try the move again. This will cause the leader to be move conscious of the lead and connection and will likely lead to a more successful lead-follow.