Watch the Emoto-Trem online guitar lesson by Jennifer Batten from Rock Sauce For Lead Guitar
Most beginners to the tremolo bar sound nervous to me. You don't want it to sound like a cartoonish "boing". Start by just getting a semi slow vibrato with the same amount of movement sharp as flat. You don't need much movement at all to get a great vibrato. Play every note of a scale pattern with a tremolo vibrato slowly. Try playing all day long with your pinkie curled around the bar, trying every possible move you can think of with it.