For example?
For the case of CDS's on MBS's, you just wait for the next recession.
Sounds easy. Makes you wonder why anyone would sell a CDS, seeing as you think it's a guaranteed winner.
It's a winner as long as you can defer the day of reckoning to the point where the problem is so big that a government bailout is required to avoid a total collapse.
Something like the S&L crisis. People were making lots of money right up to the point of systemic failure.
profit: http://www.financialsense.com/fsu/editorials/amerman/2008/0917.html
That and the political appointee of the now disgraced former governor of New York said it was ok to do it.