What causes Twang?

I think what you're after is how to come-up with Telecaster bridge tone. First of all, a Telecaster guitar is the main ingredient as the combination of that cheesey steel bridge, the brass saddles, the large apature coil (for a single coil type) pickup, the steel bridge pickup plate, and playing with a combination of pick and fingers will get you there. The Nashville cats also typically use a compressor to get a bit more punch in the tone, too. And, don't forget to use a tube amp with Fender-like tonality. That's part of the mix, too.