Quick Tip: use of the term is considered by many to be derogatory and has been largely replaced by Indigenous Peoples.
Here's a link to our free eBook Indigenous Peoples: A Guideline For Terminology that goes into detail about terminology.
There are times when it is appropriate to use the term and there are times when it is not.
There are legal reasons for the continuation of the term "Indian" - such as in the Indian Act and in some government publications. The general usage of the term is considered by many to be derogatory and has been largely replaced by Indigenous Peoples.
When referring to a community, search online to determine if they use a variation of Nation, Indian Band, or Tribal Council. It's best to go with what they're calling themselves.
And when it comes to working with individuals the same rule applies. Go with what they are calling themselves. If in doubt, talk generically about communities or nations.