I took an on-line Craftsy course in knitting lace that included instructions for blocking.  I found this part incredibly fascinating and therefore am posting photos of the process from my second lace scarf.
This first photo is the unblocked scarf with kitchen twine laced around the perimeter.  This is used for stabilizing the yarn when it is stretched.

The four corners are stretched and pinned...

Then each section is bisected to smaller and smaller sections...

Until it is completely pinned.  Then you let it dry