Now I feel weird, because I dust my little collection at least once in two months and mostly, it's even more often - I sometimes clean them up only because I've got a new pony or sold a pony or got tired of the way the G2 babies are lined up and want to see if I can mix them up a bit and then I go back to the old sequence...
I use small brushes (like the ones used for applying powder make-up?) to dust ponies and do the shelves (glass or wooden ones) in traditional ways. Sometimes I brush the hair and dust it off too - and if needed I'm giving the ponies a wash or a good clean-up with wipes, at least once a year.
Seriously, I clean the ponies and their shelves more often than anything else in my room, including my jewelry displays.