I have printed a model that pushes the limit of the 3D printer.
The smallest part on the model is 0.5mm. The overall size is 6cm by 3.5cm. That size doesn't allow any room for a file or sander to do anything. When I received my model it had a lot of loose powder in the cracks and grooves.
To clean this up I used an Exacto blade to lightly loosen up the powder, scratching ever so slightly and blowing the dust away.
This worked for the bulk of it. Next I used a new toothbrush and violently scrubbed the model. I used a soft bristle brush first with no visible results. I then tried a firm brush and received my desired results. Finally I painted the model with Testor's "Model Master" Acrylics. These paints are really thin and wash up with water. I needed a thin paint to be able to retain the detail.
The next experiment will be to try and somehow sand.