Do not stop at the index, go to the source. Research in the source, read it page by page. See how the book, journal, card file, however it was kept, and then, read about the source, why was this record created, why was it kept, who needed it, who used it, where was it kept, when was it created and how was it used? Examine the handwriting to get used to it and increase legibility, check the organization to see who should be included or excluded from any subset of the data. Use the who, what, where, when, why and how questions to understand the "life and times of the source." Knowing that certain census books were copied in triplicate helps understand how and why the ditto marks are off.
I listened to my grandpa tell stories about his childhood and his brothers all the time, but never heard any military stories. He was twelve in 1917 and thirty-six in 1941 with a wife, family and farm, he was just not in the age group. Before publishing the story of the Breitensteins in Louisville, I searched for my great-uncles in the World War I Draft Registration cards. My grandfather and his eight brothers were born between 1888 and 1908. I can not imagine my great-grandmother Elizabeth Ann (Steinmetz) Breitenstein, mother of nine boys, sending her six eldest sons off to war much less to register. Technically she might have only sent off four, as Ed and Mike were married with homes, wives and children of their own at the time. Could all the parades and patriotic songs in the world cover that angst?