Bleeding them is a must.
Salting and wrapping them in newspaper works.
A friend of mine salts them heavily and pops them in an old margarine tub just like that, works ok.
Best method in my opinion is dissolve salt in a jar of sea water, keep adding until the salt cannot dissolve anymore. Then just pop your bled worms in and freeze. I've caught good fish with this, and the worms still look pretty good / fresh once defrosted and ready to rig on your hook. Works very well with Wonder worm too, and even prawns believe it or not.