Give it a good vacuum with the vacuum cleaner, and then if you have one of those hand held steam cleaners take that over it and concentrate on the edges, then once it has had a good airing and doesn't feel damp turn it over. It's a good idea to vac your mattress regularly and when you change your bedlinen it's a good idea to leave it uncovered for a while before you put the fresh linen back on it
also make up a spray of 10 drops of eucalyptus oil, 10 drops of lavender in a cup of water and 'mist the surface and allow to dry its supposed to repel dust mite