I try looking through the whole list of possible matches when they first appear (normally when you enter a birth date) Look for ones which have a birth place which is compatible with what you know of the family.You might want to check those, but if you don't see anything likely enter the death date. At least in my experience so far, all or almost all of the possible matches disappear at this point and if there are still a few possibilities, most of them can be eliminated quickly. Eventually, if you're working back a line, you likely will find a clear match and then you just need to enter the WikiTree ID at the top and you're done. It's the rare case where you can't tell if you have a match or not and have to try contacting the PM if there is one. In my experience it's less than 1% of the time and if it does happen, it's a sigh that it's time to switch to a new line while you're waiting.