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 sist
I've said before that creating a timeline is very helpful when trying to break through a brick wall. Not everything can be written down on a timeline, though. What else do you know about an ancestor? Write these things down as well as perhaps using an itemized list at the bottom of the timeline. Everything helps when you are searching.