This one is probably the easiest question to answer - use it! The number 1 way to break in you sling is to just jump in and start using it. Just like a new pair of jeans, a new scarf or a leather bag your sling just gets better with use. Washing your sling, tossing your linen sling in the dryer, steam ironing does wonders for softening, too.
We do have one fun trick that we love for quickly breaking a Simple Silk - we call it a Cold Water Vinegar Dip and the video below will show you just how to do it!