Peter
As far as the left hand is concerned, your finger position depends on where you were before and where you are going to next. For some common chord changes, you will discover the best fingering (for you) that will make it as smooth and easy as possible. Everyone is different. Some people don't like to barre strings, while others can skip a string and bar the others. Each song will present different patterns, but you will see that some of them will become very familiar.
For right hand picking, a good place to start is the thumb plucking the G string, with the index on the C (or whatever is the next string played) followed by either the thumb or another finger. Some people use just the thumb, others the thumb/ index/ middle, and some even thumb/ index/ middle/ ring. Some people just rest their thumb on G, index on C, middle on E and ring on A, and just play the strings as needed. However, the most efficient playing (meaning for fast playing) can be aided with the idea that alternating fingers play faster than repeating the same finger twice on the same string. So, if you have two consecutive notes on the same string, you might want to play the first with the index, and the next with the middle. That said, the thumb often plays consecutive notes, since it would be awkward to alternate between thumb and finger on the same string.
I hope that wasn't too confusing. It is based on classical guitar technique, and I am sure there are other methods as well.
–Lori