Many headsets go into pairing mode automatically the first time you turn them on. So the first thing you'll want to try is just turning the headset on, which is usually done by pressing a button. The Jawbone Prime (pictured here), for example, turns on when you press and hold the "Talk" button for two seconds. BlueAnt's Q1, meanwhile, turns on when you press and hold the Ant button on the headset's exterior.
If you've used the headset before and want to pair it with a new phone, you may need to turn on pairing mode manually. To activate pairing mode on the Jawbone Prime, you need to make sure the headset is turned off. You then press and hold both the "Talk" button and the "NoiseAssassin" button for four seconds, until you see the small indicator light flash red and white.
To activate pairing mode on the BlueAnt Q1, which supports voice commands, you put the headset in your ear and say "Pair Me."
Remember that all Bluetooth headsets work slightly differently, so you may need to consult the manual that came with the product you bought.