Baptisms and Marriages
Always look to the baptism of children for godparents or witnesses to a marriage. Many times they are members of the family. I was able to find the parents of a groom or bride by researching the witnesses. One baptism listed the godparents and so I researched them. They're not always married but in this case they were, even though it was not known because the female was listed under her maiden name. Then by looking for that marriage, I discovered that the bride was a sister to the father of the baptized child. That helped me identify his parents because the bride's parents were listed in the marriage document.