The little things can certainly trip you up in Revit. Here are a couple of quick tips.
When importing a CAD file (such as an AutoCAD drawing) for use as the basis of a site plan or topo, be sure the Current View Only check box is NOT selected. Otherwise, you won't be able to select the drawing for use in creating a topo surface.
However, the opposite is true when importing or linking a CAD drawing for use within a drafting view. In order for the CAD file to be visible in the drafting view, it SHOULD be imported or linked to the Current View Only.
Also, remember that after placing the CAD drawing in the view, you can move it to the foreground or background by selecting it and then choosing the desired option on the Options bar.
Paying attention to these small details can help you avoid some frustration.