You can help this with rel canonical:
https://support.google.com/webmasters/bin/answer.py?hl=en&answer=139394
canonical is not a cure-all though, and I’ve encountered many sites where things are still viewed as duplicates despite having canonical being configured properly.
Ultimately anything that is tagged with multiple tags or placed in multiple categories will be duplicates in some sense. Be sure the category title is different and unique, and there is some pagination in the page title.
It’s hard to avoid completely without using noindex on some category & tag pages, but obviously that doesn’t make sense in every situation.
