BEST PRACTICE FOR 2D CAD
Don't IMPORT DWG or DGN files. They will bloat Revit and add extra linestyles and line patterns. LINK instead.
Link to Current View only (for 2D CAD). Copy to other views if needed.
Consider placing CAD files into their own linked Revit file. Set up views in this Revit file that show CAD files the way you want, and use view By Linked View in the main Revit file.
Don't EVER explode CAD files in a main Revit project file. If you want to turn a CAD file into a Revit file do it in a separate Revit file and link that file. You can also import a CAD file into a family template and save it as a family (e.g. a Detail Component family template for for details).
Don't rely on CAD files in your Revit project forever, work toward native Revit details and detail components.
BEST PRACTICE FOR 3D CAD
CAD imports are not cuttable by Revit - they appear as elevation in sections. To make them cuttable import (you can not use link) the CAD file into a new Generic Model family. Then place that family into the project file.
If you want to use the CAD as a Mass, link it into a new Mass family (note walls, roofs etc. can be hosted on a Generic Model).
POTENTIAL PROBLEMS WITH AutoCAD FILES IN REVIT
Corrupt linked DWG files.
Large file size and extraneous information.
Linked CAD can become unlinked but will still display. This can cause confusion as to what the latest file is.
Possibility of someone exploding, causing up to 10,000 extra elements.
Many AutoCAD layers and linetypes are brought in after an explode.
Visual clutter.
DWG files from programs like AutoCAD Architecture and Civil 3D may need special plugins to see all of the data.
AutoCAD IMPORT/LINK ISSUES
Run AUDIT on AutoCAD files to make sure they are not corrupted.
Purge all unused layers.
Size of CAD needs to be under 20miles (32km) in extents. Do a zoom extents in AutoCAD to check there are no stray entities.
Revit only recognizes the World Coordinate System (WCS), and will only bring CAD files in at WCS. Remove all UCSs.
Splines will be rubbish in Revit. Convert all splines to polylines.
Polylines in AutoCAD can cause problems in Revit. If a CAD file isn't displaying properly try exploding polylines in the AutoCAD file.
Revit imports from Model Space unless there is nothing in Model Space. It then asks if you'd like to import the stuff it finds in paper space.
Revit doesn't "see" AutoCAD points, doesn't snap to them, you'll see them but can't "use" them.
Revit doesn't "see" or even show AutoCAD Xline or Ray elements.
Save details as single cad files, not composite "sheets" of details. Single cad files can be added to individual drafting views and added to sheets allowing Revit to keep track of the sheet and detail numbers for us.
EXPLODING CAD FILES
As mentioned above don't explode full drawings. The only reason to explode a CAD file is to turn a CAD block into a Revit family, which you do in a new Family file, not a project file.
Revit has a minimum line length of 0.7mm. Any line shorter than this well be deleted when a CAD file is exploded.
They will also be deleted if you use the scale command to reduce the size of the CAD import.
If there are Reference Planes in the file lines from the exploded CAD import will constrain themselves to them, even if not very close to them. What happens is if any reference planes are moved seemingly random lines of you exploded CAD import will also move. Best to have no reference planes except for Center (Front/Back) and Center (Left/Right). You could also turn lines into filled regions or masking regions.
You can turn lines into Filled regions or Masking regions by selecting them, Copyclip. Creating a new filled region or masking region and Paste aligned to view. You may find the CAD lines don't form a closed loop, or there are lines on lines. You need to fix these problems before Revit will let you finish.
Exploded CAD lines use their layer name as their subcategory name. Make sure you change the lines to a Revit subcategory and delete the CAD subcategories.
Make sure you purge. The CAD import remains in the file until you do.