There is such methods if you searched on it in search engine of the forum you will find guide. But i will tell you my method i know :
First of all : If you prefer it for tracing then it is favorable to make independent worksheet to do that:
1-click on worksheet and from navigator map on the right side of the programme click on make new independent worksheet.
2-Then You have two options to import it after you become on the worksheet you made
a: From File menu:File special --Merge --select extension DWG
b: From File menu :File --External content--place external drawing and select DWG
after that you should activate trace &refrence and make the worksheet is show as trace and refrence, So you can snap it from floor plan and Then you can deactivate show as trace and refrence to see what is the work done.
Here is some useful links that may help you :
http://www.archicadwiki.com/DWG/Import