Don't forget simple Google. As was said with Ancestry, you have to find multiple sources (that are independent, not circularly reporting the same bad fact), to confirm.
I've been using genealogical research in my investigation of the 1813 Gutierrez-Magee Expedition. The regular historians had basically drawn a blank on who these guys did, as archival and primary source data was so limited. So I started doing basic internet research and found a lot of angles that you would never find otherwise.
Google brings in all sorts of sources, including the vast numbers of scanned books that Google has made available, which are text searchable. There was one guy in the Gutierrez-Magee Expedition named Darius Johnston. Some amateur researcher had guessed on a lark that he might be related to Albert Sydney Johnston, but others dismissed it because they had a supposed list of A.S.J. brothers and he wasn't on it. I delved deeper and discovered an old Johnston family history book written in the 1890s that was rare but had been scanned and digitized by Google. In it, I discovered that A.S.Johnston's father actually married 3 times and the "official" list of his brothers that someone was citing were only his full brothers. This guy who had fought in Texas in 1812-13 was actually Johnston's way older half brother. And then, with a few clues of things to search, I discovered a SECOND brother of A.S.J. who fought in Texas in 1813. I've never read a bio of A.S.J., but I don't think any one of these mentions the fact that when he was 7 years old, his two older brothers were fighting in a revolution in Texas. That's kind of important to the story of how A.S.J. decided to come to Texas.
A second story, which I've already related on another post, is how I cracked the code on who Augustus Magee (the leader of the Gutierrez-Magee Expedition was). His entire pre-expedition biography in the Handbook of Texas is one sentence with 4 factual points, 3 of which are wrong. I was able to break open a whole bunch of information after experimenting with various google searches. Knowing he went to West Point, I put in all sorts of search terms in with his name. Some with his full name, some with his first and last, some with just the word Magee. Finally, I put in "Augustus Magee" and "cadet" and 20 pages in on my search results, I came across a document that proved he had been a "cadet" at a preparatory school. That gave me a clue to who his family might be and I was able to blow open the door after that. Remember that one sentence in Handbook of Texas? I've now got 20 pages or new research on Magee sitting with an editor at the Southwestern Historical Quarterly awaiting review.
The point being that I did all of this through straight google searches. Take the name of your ancestor, or every potential misspelling of it, put it in quotes or reverse the first and middle names, etc. Toss in key words related to their profession or some town, or if you know the name of a ship, or whatever, put that in. Take any piece of evidence and explore it fully. Did he live in X town? Who were his neighbors. Frequently, when a family pulled up roots in North Carolina and moved to Texas, they didn't do it alone. I found another case where the same five families immigrated from the east to Kentucky, then Tennessee, then Texas. Turns out, they were all members of the same religious sect. They traveled together, they intermarried, they were essentially a little mobile community. If somebody drops off the research face of the earth, use clues like that to develop a plausible scenario to give you a shadow of their journey, then use that information to find them on the other side.
If they came from Germany or England or wherever, look into the region they were from. Don't know the region? Well, are they Catholic or Protestant? That might give you a clue. Which areas are Catholic or Protestant? Bear in mind, they might come from the opposite sect to what is common in that area, thus a protestant in Bavaria will be an oddity, or a Catholic in Northern Germany (my ancestors), so that might be a hint to why they left. If they raised a certain crop or ran a certain kind of business when they arrived in the U.S. then that's probably the same or similar job to what they had back in the old country.
Also, if you know a foreign language, or enough to pick out key words and phrases then drop text you think might be good into Google Translate, try going to the Google website for the country your ancestors came from. There is not just one google. Google.com will give you answers designed for Americans. Google.de or google.fr will give you German or French answers.
Say you think your ancestor was a farmer in Bavaria. Put his name in and use the German words "bauer" (farmer) and "Bayern" (Bavaria).
This type of searching can be very long and 90 percent of your searches will be fruitless. But when you find a great nugget of information, you will get an amazing thrill from it. And if your searches fail, don't give up on them. Keep a log. Come back to them. I've searched and found nothing and then a few months later, did the same search and something new came up due to a new document being scanned, a new blog post or just the algorithms "learning" from your search patterns in the intervening time.
The best part of it is that this type of research is free.