Photographing butterflies is quite challenging and the most important skill needed is patience. Butterflies have good eyesight and will often take wing long before you get anywhere near, close enough to capture them. Nevertheless, don’t chase them; this is not a sport you are likely to win. Most often, you have to wait for the right moment. Be observant and keep your camera in hand.
How you approach a butterfly makes a huge difference. Always use a slow and careful approach and no sudden movements. Lifting your camera, shifting positions etc. should all be done slowly.
Butterflies love the sun, so if you cast a shadow on them, they will usually fly away.
Butterflies, just like people, have different personalities. Some are easily scared by human approach while others are more tolerant. Focus your photographic efforts on the latter.
To know your subject really helps! Learn about their preferred host and nectar plants, study their behaviors and become familiar with their favorite hot spots.