Watch the Using the Pick online guitar lesson by David Hamburger from Blues Guitar For Beginners
You'll notice different guitar players have different ways of doing things, from how high or low they strap on their guitar to how they hold their pick or strum the strings (all wrist? all arm and shoulder?). There's often more than one way to finger a chord as well, depending on either the musical circumstances, the individual player's preference, or both. The A fingering here makes switching between A and D easier.
>>Basic Open Position Guitar Chords