Depends on what side of your industry that you want to build. Commercial = phone call, you have to get in front of the decision maker, they know you are coming they have set time aside for that appointment. I cant comment on dropping leaflets in, personally I would have thought letters would not be the way to go, you need the attention of the buyer. He takes time out of his schedule because he knows you are coming - like in any buying process.
Dropping leaflets or cards, I dont think works - who knows where they get filed?
If you feel ok on the phone and buy some data or target who you quite fancy having as a client, thats all it is really OP
Wish you luck
Hope that helps