Before adding new records, do a search over all branches on the site to be sure that the people are not already entered as part of someone else's branch. If they are already there, then you can enter any missing family members and link them to their existing relatives.
Also remember that this is a growing tree -- with other researchers adding new information, search results down the road may include more than they do today.
Under Collaborate > Find Duplicates is a report that will run across all names in your branch of the tree, comparing to the all names in the entire system, and will report back any possible duplicate records. This is based on the following:
This is one example of how consistently formatted place names are important, as "NC, Martin Co" and "Martin Co, NC" will not match as being the same place.
It is likely that this will produce pairs of people who are not duplicates, but there is not enough information for the system to determine that they are not the same person. For these cases, they can be cleared from the duplicate list by
If the pair in question could be the same person but you don't really know, then maybe leave them there as a reminder to keep looking for more information. Maybe contact other researchers for both of the people to ask the questions you may have.
Clicking a person's name will open that person's record in a new window, so that the duplicate list will stay as it is -- you do not have to keep re-running it to return to it as you continue down the list.
If your screen is large enough, you can open side-by-side the two windows for the two duplicate people, and compare their information. Then edit one to contain any additional information that the other has, and delete the other.
Resolving the duplicates is important both for you and for other researchers. If two of the same person are not merged, then you will only see part of the information, and other people browsing your information may be missing whole branches of the tree they would not see otherwise.
The list of possible duplicates will be emailed to you once a month, to notify you of ones you may not be aware of, and to remind you to keep on top of resolving them.