I've heard that you should use hard suitcases, not the soft, zippered kind. If you only have the soft kind, then put ALL your items in a sealed, XLarge space bag inside the suitcase.
And keep everything (purses, suitcases, camera bags, etc) off the floor and beds. Use the luggage rack instead (after checking it).
When you get home shake all your clothes (in the suitcase) outside before throwing them into the wash.
Good luck.