Make your bed up! A made up bed not only is aesthetically pleasing and improves your state of mind but it also keeps the dust mites out and your bedding.
Keep your bed clean of clutter and don't use it as a table! Bags, shoes and even clothes that are dirty can transfer unwanted germs and oils on to your bedding.
Keep your room cool and dry to avoid unnecessary sweating secretions on your sheets.
If you want to extend how often you wash your sheets instead of every week, try showering in the evening as this may reduce the frequency of washes and therefore prolong the lifespan of your bedding. And the bonus - a night time shower relaxes you and amplifies the incredible sensation of slipping into fresh clean sheets!
This one is the toughest - try a few days or completely make your bedroom a no pet zone; our furry friends shed fur and skin cells which feed the dust mites. If this is an impossible task (like it is for us!), stick to the rule of washing your bedding weekly!