One thing I've discovered over the years is not to ignore the names of witnesses on marriage entries, these can often lead to discovering other family members, or help to confirm you've got the right person. To give a few examples from my own research:
I spent a long time trying to track down my 3xgreat grandfather John Green Sayers' brother Thomas after he appeared on the 1841 census with his parents and brother as a 5 week old baby living in Grimsby.
By 1851 their mother Harriet was dead and their father, a mariner was away in Dover. John was living with his grandmother Mary and her 3rd husband Benjamin Willman as their son John Willman and his younger brother William was listed as William Sare grandson.
There was no trace of Thomas, no matter what search I did I couldn't find him in the 1851 census, so I checked the death indexes and burial entries for both Grimsby and Hull to see if he had died, but still no luck. Looking for John Green Sayers or John Willman in the 1861 census, I found him living at 8 Chapel Lane as John Willman with his wife Nancy and his occupation given as Sloopman. With John continuing to use both Willman and Sayers almost interchangeably, it took me a while to find his marriage in the General Register Office (GRO) indexes; but find him I did marrying Nancy Fish on 14 November 1859 at Hull Holy Trinity church, and one of the witnesses was Thomas Sayers. Could this be our missing brother?
If Thomas were alive and attending his brother's wedding in 1859, then he should be on the 1861 census, and a search revealed him on board The Humber in Victoria Dock, Hull as a 19 year old apprentice; and I've been able to find him on every subsequent census since then until his death in 1895. Though I still can't find him on the 1851 census, no matter what I try and the only conclusion I can come to is that he was with his grandmother and brothers but for some reason was missed on the census.
More recently I've been trying to discover what happened to the two sons of Mary Grant and Richard Amos, Mary whose first husband was John Green had two children with John, Harriet who later married Ethelbert Peter Sayers and John; she then married Richard Amos and had two boys Richard and Charles before marrying for the third and final time to Benjamin Willman. The boys were living with Mary and Benjamin in 1841, but by 1851 they had left home, whilst checking indexes and the IGI, I found a marriage for a Charles Ameers at Holy Trinity Hull in 1859 to Martha Satchell and as I had previously seen Amos written as Amers I thought it was worth checking it out. A visit to the archives in Beverley, East Yorkshire gave me the opportunity to check out the entry in the parish register, which I found for 27th December 1859 and one of the witnesses was John Green Sayers, the other his wife of 6 weeks Nancy; giving me confirmation that this was indeed the Charles Amos, or Ameers as he seems to have preferred his name to be spelt, John's half-uncle.
Charles also gives his father's name as Benjamin Ameers Sloopman, instead of Richard Amos/Ameers sailor Benjamin Willman being his step father.
And a final example from this family. In 1883, John Green Sayers married Eliza Baker at Holy Trinity in Hull. It took me awhile to tie this Eliza Baker up to my 3xgreat aunt Eliza Green who was born in 1831 and was the younger brother to my 3xgreat grandfather JamesGreen 1820 - 1854. Eliza had married several times, inlcuding in 1868 to a James Baker. It was only when I received the marriage certificate for her wedding to John Green Sayers, did I tie it all up, not only was Eliza's father down as Thomas Green, but one of the witnesses at the wedding was Leonard Farrow Green, the grandson of James Green. This also answered one of those questions we often ask ourselves how did our grandparents etc., meet; well in Leonard's case he married Ethel Roseman Sayers daughter of John Green Sayers and Nancy Fish and step daughter to Leonard's great aunt Eliza.
These are not the only examples I have found in my family and others, where the witness at a wedding has helped to confirm a relationship. Sometimes I feel family history is a great big jigsaw and we have to put the pieces together - these kind of discoveries can make all the differences in getting the right pieces to fit together.