if you have a marriage certificate usually the mother's name is on there and just underneath it states nee with a different name. For example Jane Brown father John Brown mother Mary Brown nee Smith then Smith is the mother's maiden name. I also found that in my family people had the mother's maiden name as there middle name. You might also find this information on a birth cetificate. This information might depend on whether you are looking at English verses Scottish certificates.
Hope this helps