Continually push the stakes higher and higher. Some very successful authors write from a simple plotting. They know how their book is going to start and how it is going to come out, then they dive in. But, as most of them will admit, the basic plot is in their head when they start, although their ideas may change some as they go along. In your book, begin your story where the action begins.
Most stories start way too soon.
Work the back story into your manuscript a little at a time, don't bombard your reader with information. And want to read more. Sleepless in Seattle, etc. Magnify their faults and attributes. Most of all, make them real.