The original book has a bit of a half-hearted show within a show concept. As written, it wasn't just the story of a group of senior citizens stealing furs to buy and renovate their hotel, but it also has scenes and songs showcasing and highlighting the actors you are seeing performing that story. So songs like the opening "Old Folks," "Broadway, My Street," "Coffee in a Cardboard Cup" and "Go Visit Your Grandmother" are not plot driven, but are turns to feature and celebrate the eldery performers. The London production from a few years ago featured a revised book that attempted to integrate all of the songs, and remove the "actors performing a show" concept, to minimize the confusion factor.
That said, I worked on a production of "70, Girls, 70," using the original book, and the audience went berserk for it, flaws and all.
Begin at the beginning and go on till you come to the end: then stop.