Having started some years ago with Samuel Pepys, I like Claire Tomalin's biographies, which strike a good balance between the accessible and the academic.
She gives an excellent depiction of Jane Austen and the family and social setting that shaped her. I came late to Austen - I remember a near rebellion at school when her books were chosen in preference to Ernest Hemmingway's for Sixth Year Studies English, and I only got around to reading Pride and Prejudice after seeing the Jennifer Ehle/Colin Firth version. P&P certainly gets my vote as the best English novel; Tomalin, however, prefers Mansfield Park which I have to admit I thought was a tale of unsubtle moralising, although she discusses the debate and certainly opened my eyes to some of the issues under discussion. I did not appreciate at the time, for example, that a play on words in Mansfield Park about the Royal Navy's "rears and vices" was in fact a reference to sodomy! Austen may have been a maiden aunt, Tomalin says, but she was not unaware of the ways of the world.
The book gives an insight into the lives of, for want of a better word, the middle classes of the late eighteenth and early nineteenth century. It was striking, for example, just how many of Jane's sisters-in-law died giving birth to a tenth of eleventh baby.
If you like Jane Austen's work and want an interesting but easy introduction to her life, read this.