Though wool is a springy fiber, after long use it may tend to mat down a bit. To restore the pile to its original state, brush it up with a coarse brush. The coarser the brush the better. Wire brushes work best and do not harm the fleece.
Wool fleece is a natural fiber and resists soiling, this simplifying cleaning. In most cases spot cleaning in place with warm water and mild soap is all that is needed.