This section assumes that you have already attached your strap.
Sit in a straight backed chair with no arms. Hold the mandolin in front of your body, and look down to see where your right hand falls naturally – without your trying to move it to a specific spot on the strings. You will usually get the best sound if you pick somewhere between two inches on either the end of the fingerboard. (Meaning, picking on the end of the fingerboard, or just past the end of the fingerboard where the strings have nothing below them.) In order to have your right hand go automatically where it needs to go, without your having to look at it all the time, you may need to shift the mandolin to a different spot on your body. Some people set the mandolin on their right thigh, and others hold it in the center of their body, and some hold it more to the left. But find a place that, when you hold the instrument in front of you, your pick will automatically end up somewhere within that four-inch range specified above. Again, there is no right or wrong spot to hold your mandolin, as long as you produce a good sound and achieve a playing style that is comfortable for you.
The proper angle for positioning the neck is another topic that is passionately debated among mandolin players. I've observed a number of mandolin players who position their necks at completely different angles – and they're all excellent players in spite of it. One very famous player puts the neck almost to his shoulder, and another moves the neck down to the level of his hip. And, of course, there's everything in between. Rather than picking an angle and feeling that you are required to use only that one position, try experimenting with different angles to see what produces the best sound for you. And remember that this may change, as you become a better player. But in order to produce the best sound, your pick must strike the strings at a perpendicular angle:
To understand what I mean, try striking a string with your pick turned sideways:
Did you hear the difference in the sound?
The important thing is to accommodate your right hand, which is more important than your left. When you begin playing, you may hold your neck at one angle to allow your right hand to strike the strings at the proper angle. As your right hand grows stronger and begins to develop more motion, such as the tremolo, you may have to change the angle of the neck so that your pick continues to strike at the proper angle.