Sort out everything in the house you don't want and do a bootsale for a start. Or if its really decent stuff sell it on Ebay. It soon develops into buying stuff to sell. I make a nice bit extra selling on Ebay plus you are still home.
If you've got little ones, sell some of their clothes which they have grown out of. Most little ones barely wear some things so you might find you can make a few bob selling almost new clothing.