Watch the Finding Kick Drum Sounds online guitar lesson by Ben Lacy from Two-Hand Groove Guitar
I begin by showing you how to find a cool kick drum sound, using either hand. First, mute the strings with your left hand index finger. Drape your finger where you don't hear a harmonic. Hit the strings with your left hand middle finger, or your right hand thumb.
Be sure to hit the string strong enough to get a good sound, but not too hard. Don't kill it! If you use your thumb, don't lift it too far from the string.