Soft playing is probably the bane of most of our existences and something we constantly practice executing consistently. In a perfect world, playing soft would be a piece of cake, but there are some misconceptions that usually deter us from actually achieving softer dynamics. When I first was introduced to how soft "soft" actually was, I had never heard it done in the context of "auditioning." We've all been there where we get caught playing "practice room dynamics" in a large hall, and my instructor, Doug Waddell, encouraged me to expand my dynamics immensely. He demonstrated what soft actually was and I was very taken aback. How could I ever play that delicate? My hands are shaking, how could I control the stick at those low heights?
I personally think, much like getting used to the silence before you play, we have to get used to the volume of what actually soft is, both in the context of the practice room and a bigger hall. If you can play super soft and clear in a small practice room, you definitely will be prepared to demonstrate a range of soft dynamics in a concert hall. So, accept that the soft dynamic is a comfortable one, something you expect to hear as you play and don't shy away from it. The worst thing you can do is to be timid at the sound of you striking the instrument; even though it is soft, it should still have presence and fullness of sound. So, get used to how soft "soft" is in your mind and your ear, expect it, welcome it, and you will lose that timid approach to it.
Now, actually playing soft, again in a perfect world, the soft strokes should just be a very small version of a comfortable louder stroke. Study how you play rhythms at a more comfortable dynamic. Notice that you play fuller strokes, taking no prisoners with your approach, accuracy and clarity. Now, how do you translate that stroke and style in a lower height? An exercise that helped me with this was to play the rhythm or pattern at forte for 2 minutes straight, or until it is comfortable and easy. After the two minutes are up, take the dynamic down and repeat the exercise. You do this until you get to your soft dynamic threshold. The more you can find that similarity between the louder and softer dynamic strokes, the easier it will be to execute the soft dynamic with any rhythm. Stay loose, especially as you get softer. The worst thing you can do is tighten up as you get softer.
Again, I really think that playing soft is based more in being comfortable with the sound, not being shy about playing the note, and actually playing full strokes, as full as your loud ones. Release any unnecessary tension, especially in multiple bounced strokes and faster singles as you play soft (sometimes it results in losing the control or ghosting/over playing some notes). Take your time, maybe try just single notes until you get comfortable hearing just those notes, and build your confidence enough to play more notes and more patterns. It's all about getting comfortable in your hands, ears and in your head (in reverse order), and the easier you believe it is, the easier it will be. Happy Practicing!