Gerbils are very clean animals and if kept in pairs or groups will spend a long time grooming each other. Even a single gerbil will spend some time keeping itself clean. The act of grooming reinforces the bonding between the pair and also the dominance within a group of gerbils.
As they are so clean, they require very little help from us, however you can provide them with a dust bath with loose dry sand in it that they will roll in. The sand should be placed in a bowl or other suitable container and should be removed once the gerbil has finished, otherwise it is likely to be used as a toilet!
Grooming powder can also be used on gerbils to remove any stains, particularly if you enter your gerbil into a show, where cleanliness is very important.