I had never tried them before, so thought I'd give it a go...
Remove the ribs/stems. Put into water, pull out; repeat (I do it 3 times). Roll the leaves up, slice, then rough chop.
In a stockpot, I put a large smoked ham hock, and the root end of an onion (what was left from dicing onions for the stew); covered the meat with water, added the collard greens. It takes awhile for the greens to become tender.
When tender, I added one can of rinsed and drained garbanzo beans.
I served this with the chicken stew, put the leftovers into the stew, reserving the ham hock for another use.