Ok, here's my latest trick. I sit at the piano with tuner in front of me. I play the note on the piano, close my eyes, sing the note,then look at the tuner to see if my vocalisation is in tune - this is actually the toughest part for me. Then I close my eyes and play the long tone, then look at the tuner to see how close I am. The more I do this, the more often the long tone is right on the money and steady (I quickly adjust it if it isn't). It really amazes me that one can learn to blow a note within zero cents of a heard pitch. I wonder if string players could benefit from and exercise like this.