If I was doing my own, I'd choose not to focus on the usual story that we have throughout the musical, but I'd take another characters story, and put them in the central role. An example would be the revolution, with Enjolras and the rest of the students, including Marius, being the focus of the movie, canon to the book. I'd include some backstory at the start as to the life of Enjolras, and how he comes to create the Friends of the ABC group. Later on, Marius' story would start to come into the musical as well, with him being important too.
Obviously, other characters such as Cosette, Valjean and Javert would not be as important, but they would still play roles within the movie in relation to the characters they are involved with. Cosette would come into it when we see Marius' story in more detail, as would Valjean. Javert would obviously be involved when he goes to the barricade, however a lot of the story between him and Valjean would not be included as it would not be particularly relevant to this plot. The Thenardiers would play their role, however it would be more in relation to Marius.
Some of the focuses of the movie would include Enjolras/Grantaire, as well as Enjolras/Combeferre. We'd also get to see other characters such as Joly, Feuilly etc in a lot more depth as they would be very important.
The reason is that I think it would be something new and interesting, considering the usual plot has been done a million times. Obviously we'll see the musical movie later this year which I hold high hopes for, however after that, what more can really be done on the main plot without recycling it? This gives a different take, but manages to cover the whole story in enough time for a decent movie length.
The law is unjust.