It also helps to keep a 2nd browser window or tab open to your list of all people. If the person you are about to add from the census "sounds familiar," you can quickly check the list of all people to verify.
My maternal grandparents were 3rd cousins. Had I not been extremely careful I would have had the same people in my tree many times over.
A paternal great grandmother came from Ireland with her siblings and a full set of first cousins, but without either set of parents. With Irish naming conventions the 2 sets of children had all the same given names. It took careful evaluation and comparison to determine which "Patrick" belonged to which family.