Before the internet, guidebooks were the go-to source for information. Now, however, they are really best for finding out general information about a school such as its size, location, majors, and average class size. The data that is used in the books is often requested 6 months before the book is printed, so they're not the best source for current data. School websites are better for most recent acceptance rates and tuition rates, for example.
Rankings, in my opinion, are not useful. Some of the criteria used in the rankings, for example, the percentage of alumni who give money, do not reveal any information about the quality of the education a student will receive.
Relatives can be helpful, as long as you keep two things in mind. First, if your relative attended the school more than two years ago, their information isn't really relevent. Things change from year to year. More importantly, think about the personality and/or interests of your relative. If she is really outgoing, her opinion might not be as meaningful to you if you are super shy. Or, if she's really interested in sports, her feedback might not be helpful if you're looking for schools with amazing dance programs.