When dusting, a good rule of thumb is if you can see it, the neighbor can see it. Do a walkthrough at the end of your cleaning and see if there are any major areas that have been missed. All major flat surfaces throughout the entire apartment should be dusted including items like dressers, side tables, shelves, and window sills to name a few. Failing to remove dust can negatively impact your ratings.
You can find a full overview of what the Neighbor (customer) expects from a standard cleaning here: http://bit.ly/lapa-lopa-cleaning-whats-included