Advice On Scanning Old Photographs ...

As I mentioned earlier in the summer, I'm scanning some old family photographs from my grandma's side of the family. I have not finished scanning all of the pictures, but I have been lucky that some of them were labeled. Unfortunately, there some that I do not know if there is a relationship to my family or not. In addition to the mystery photos, there are several photograph-sized negatives in the albums. Has anyone ever scanned in negatives before, and if so, are there any precautions I need to take, due to the fact that these negatives are from the '30s and '40s primarily? Any suggestions or advice are welcome. Thanks.