One of the first things I do when looking at a book is to flip to the back and look for sources. Did the author do primary research and list sources, or is it all a churn from other books? Online reviews are also good to look for, but I view all of these with a bit of suspicion, as well as my own reactions. As Barbara Tuchman said, "Let the evidence guide the research. Do not have a preconceived agenda which will only distort the result."

Keep an open mind and yet be skeptical at the same time, cross reference, and you'll probably do fairly well in learning things accurately.

Basically the best way to go about it is Peer reviewed articles, and trusted text books. Also just look for patterns, they often appear for a reason.

Edit: look for primary source docs as support for information too.

In addition to the other very good answers, one thing I like to see with a credible source is that the person seems to know what they don't know. Often well informed people are humble about the limited surface area of their knowledge. Another trait I like to see is that they are charitable with competing points of view. I don't mind if the writer explores a niche point of view but they shouldn't do so by dismissing or disparaging the predominant theories or advocates. A good presentation of a novel interpretation is self-aware of its position against the grain.

In short, humility over hubris.

-Author credentials

Who paid this guy to write the book? Does he win awards? Are the awards real or bogus? What do you know about the foundations that paid him to write the book?

-Source Materials

Is he quoting other history books? Is he using primary sources? Can you find a copy of the primary source?(lots of times good historians add tables of data or reproductions of their primary source material in the document they've written.

The more you learn with a critical mind, the greater your framework grows, and the greater and better structured your historical framework becomes, the better your bullshit detector becomes. One thing I like to do is read book reviews prior to reading the book so that I know what historians have already said about the book, so I can look for those pitfalls or strengths, and see if I see the same thing, am confused by the claim, or outright disagree with the reviewer.

A big thing to look for, usually in the early chapters of the book (typically the first) is for their familiarity with the historiography (history of the history) of the subject they speak of. What you're looking for is comprehensive reading of the historians that wrote in his subject prior to him.

I said "him" throughout this entire response, but that's simply because the majority of the books I remember evaluating were written by male historians. The best teachers I had were female, and many of the books I read were written by females. I just used male pronouns because I wrote this kind of informally.

Follow up question

Is the common idea "history is written by the winners" actually true?

Who tells the story from the loser's point of view?