Make it a practice to vacuum your mattress every time you change the sheets or for once in every three months.
To protect from dust mites or other allergens, you can make use of mattress covers. These need to be easily washable and removable. This will also help in reducing the frequency of vacuuming the mattress.
Get a mattress pad for placing over the mattress cover and under the sheet of bed. Apart from comforting you, it also gives an extra layer of barrier between you and mattress. This is easy to be removed and laundered. It is an ideal way to prevent your bed from getting wet, especially in houses with infants or children.
To kill dust mites, wash your bed and mattress covers with hot water frequently. To get rid of odors and soften the sheets, add half a cup of white vinegar while washing.
Keep flipping your mattress for about once in a month or once in three months. Make sure to flip it upside down as well as rotate. This will allow even wear and tear of the mattress and will also prolong its life.