Collect and compare as many different published versions of the subject as you can. Often there is one old surname genealogy and/or a “dictionary” of settlers. Then there will be some accounts of different branches in some “all-my-ancestors” volumes (often seen in Torrey’s New England Marriages Prior to 1700 – see the new version of Torrey on americanancestors.org that now takes you to the image of the full page from the book, allowing you to see and print all of the entries with the same surname together.)
“All-my-ancestor” works – the best example of which is still Mary Walton Ferris’ massive two-volume treatment on the ancestors of Vice President Rufus R. Dawes, Dawes-Gates Ancestral Lines, a Memorial Volume… (Milwaukee: privately printed, 1931–43) [available in digital form online in various places such as hathitrust.org and ancestry.com] – usually treat only one line of descent from an immigrant ancestor, but they very often provide updated accounts and sources for the first one or two generations and can save you a lot of updating effort.
Then there will likely be some published additions, extensions, and/or corrections in the major genealogical periodicals, such as The New England Historical and Genealogical Register. Keep up with what is in print by accessing periodicals on americanancestors.org and through source indexes like New Englanders in the 1600s: A Guide to Genealogical Research Published Between 1980 and 2010.
Once you have all the different versions you can find together, start typing everything into a “dump” draft with footnotes, noting differences among the accounts. See which ones were copied verbatim from earlier versions and which ones add new information. Highlight dates, places, questions that need to be checked out. My dump drafts look like rainbow beach towels with all the different color highlights, but they give me a visual idea of how cohesive (or not) the sources are. Also, look for missing sources such as probate records, deeds, church, and town records, highlighting questions about them – e.g., Probate Plymouth County? Middlesex Court Records? Findagrave? – and see what you can access at the library or online (the first two mentioned, of course, are on americanancestors.org).
You obviously won’t be able to verify everything, especially when working in areas and times that have few available sources or where the references are to obscure, unpublished, or private records you cannot easily check, but making a habit of “auditing” the things that you can access will give you a feel for how to judge which sources are more (or less) reliable than others.
P.S. I need ideas for post topics. Let me know about the types of problems with which you are dealing, and I will see if I can come up with something helpful.