Joe is correct. For the most part, you want to be subtle, so the target can't go to the cops, and get you on extortion charges.
However, there are times when being a bit more... blatant can go a long way. If, for example, they turn you down for the 'favor' you asked of them, and you get into their place, kill their favorite pet, put the head under the covers of their bed while they are sleeping in it, and get out without waking them or setting off any alarms, then that makes one HELL of an impression.
Another great trick is to call their private line while they are walking out of their building towards their car. You ask them for the favor, and they refuse. As you are telling them how disappointed you are in that decision, their car blows up while they are safely out of the blast radius. You ask whether they are OK, and if anything's the matter, and play it from there.