This is a fairly big subject, and it takes time to learn what is available for each county or family we study. It also depends a lot upon which type of information you have to start with.
I presume most people will be starting by looking for whatever parish registers, wills, old newspapers, family bibles, land records, student lists etc, they can find, because these are the types of sources we use for modern families. Wills are often very useful.
Once you have that information it is often a question of looking for whatever might be most helpful. For example if you know a person was a major land owner in a specific place, you can check the histories of that place. If you see the person has a special middle name, you might simply try searching google books or site:internet.org.
Once you actually have some decent leads you can then often start using things like old visitations, biographies, and county histories. There are also specialized publications, both books and journals.
One thing I would NOT advise doing on Wikitree is simply going to find family trees to copy from the internet, because these are often wrong. I am not saying not to look for such trees at all, but I am saying we should not simply copy them into Wikitree. Internet family trees have become a sort of virus, because internet genealogy is enormous, and they are so often copied without checks. But they often contain some kernels of truth. So check them and try to confirm what they are saying before using them in Wikitree, or otherwise we just spread the viruses.
