Feather duster, or a Swifter duster, both do a great job.
I keep my trains on shelving, most cars and a engines (60) are on the shelf of wrapped in cotton washcloths, keeps them dust free and no finger prints.
The shelves are covered with sheets to help keep the dust out, in an unfinished basement.
Real efficient, inexpensive, I've been doing this for over 25 years and its easy and works.
I don't keep many trains on the layout, change them about once a week.