Seriously though ... i have always used a lens blower followed with a lens cleaning tissue impregnated with Isopryl aclcohol.
This leaves a slight residue which can be washed off with a little distilled water from a misting spray bottle.
Like Starler says thou ... dont let the water get inside.
let air dry or blow off with a hair dryer.
I only do this if the eyepieces have lots of fingerprints & skin oils on them (public viewing nights
)