Mites are really hard to see, but their damage is often characterised by finely spotted or mottled leaves (particularly older leaves), fine spidery webs (for spider mites) and a general lack of lustre in plant leaves. They can also deform new growth.

Mites are hard to treat. Keep plants healthy. Mites often thrive in dry dusty conditions, so hose foliage hard occasionally. There are predatory mites available though you have to identify the mite, and soap sprays can work.