Personally, I dislike using commercial air-fresheners, which often contain some nasty chemicals such as benzenes and phthalates. Products with antibacterial powers, such as Febreze, are useful for items such as the dog’s bed, but simply making the air smell sweeter doesn’t really require bactericides.
Obviously, your main treatment for stale smells is to open the windows and, if you can, put a fan on. Failing that, however, this home-made air freshener will work wonders. Spray it on all fabrics, plus a few squirts into the air generally.
30 drops of citronella oil
30 drops of lavender or lavendin oil
20 drops of clove oil
A slug of vodka (to blend the oils)
Mix the first four ingredients, place in a spray bottle and top up with water. Shake as you use, to blend the oils. You can choose another blend if you like, but this blend smells good and is cheap. In the cold and flu season, I often add a further 20 drops of eucalyptus oil to the mix.