The best practice that we have found to do this is to bring the CAD file into a seperate Revit file (Drafting View).
Revitize the CAD drawing and do a purge. This will not get rid of everything that is brought in from the .dwg file but when you later bring this into your current Revit file it prevent unnecessary Revit items from coming in.
After you have your CAD file Revitized, go into your current Revit file and go into the File menu and select "Insert From File" then select the "Views" option and select the Revit file which you just created from the CAD drawing.
It is generally not good practice to bring these CAD drawings into your current projects since it is rather difficult to get rid of CAD elements and in some cases not possible.
There are other things that you can also do to keep your computer from being bogged down, such as:
Keep all hidden windows closed as you are working. This is a good idea to do before a save as if ithey are not closed, Revit will regen all these windows upon opening.
Purge your file a few times a day. You can always reload what you might need later, also helps with the file size.
Last, Audit your drawing upon opening about once a week, maybe a little more. The slow opening times are worth more than the time wasted waiting for a corrupt file to be recovered.
Hope this was informational.