If you haven't read anything by Zadie Smith, I highly recommend finding White Teeth, her debut novel, and diving in. Smith wrote White Teeth while still attending university, and it was published to great acclaim when she was only 25 years old. It's a wonderfully sprawling novel, by turns wry, satirical, and poignant, crammed full of vibrant characters, multiple themes and threads, and brilliant, surprising language. It deals with the cultural clashes and changes of immigration, generations, and class differences.
If you read White Teeth and didn't like it, stop right there; you're not going to like anything else by Zadie Smith. I loved White Teeth - despite its strange and problematic ending - and I'll probably follow Smith down any literary path she travels.
I've just finished NW, Smith's fourth novel. NW is another polyphonic trek into northwest London, and it is another masterpiece. The book is full of finely drawn, fully realized characters, startlingly vivid writing, and shifting points of view. The literary critic James Wood, who loved this novel, has called Smith an "a great urban realist", but I feel that sells her short. There is no doubt that Smith is a genius at capturing the complicated, multi-layered, gritty and often beautiful realities of life in a great urban city - no small feat. But she is also a genius of the human heart, of motivation, of self-identity, of inner conflict. Ultimately, for me it is not Smith's London that makes me recommend her so highly. It is her people.
Like most novels I love, NW is not plot-driven. It is not a page turner; it is a novel in which many readers would say "nothing happens". Depending on your tastes, that may be warning or recommendation.
I have also read and greatly enjoyed Smith's On Beauty, which, among other things, is a modern retelling of E. M. Forster's Howards End. (I didn't know that when I read it, and it's certainly not necessary to know Forster's novel in order to appreciate Smith's.) I haven't read Smith's second novel, Autograph Man but it's on The List.