If you are interested in sampling a Terry Pratchett novel, or Discworld book, many would recommend this as the one to try first. It may not be the very first Discworld book, but that doesn't matter. It spoils nothing to start with this book, and I'd be amazed if you didn't love it.
Everyone I have spoken to who has read this book has agreed with me; it is absolutely brilliant. Brilliant fantasy and hilarious comedy rolled perfectly into one.
This book introduces you to Captain Vimes and his Night Watchmen who guard against crime in Ankh-Morpork.

Vimes is easily one of the most popular characters of Discworld due to how deep and real his character feels and how easily the average human being can relate to him. To read his story is a privilege. Watch him attempt to transform himself and his guards from incompetents into heroes to save the city from an unforeseen threat before it's too late, and laugh all the way through. Simply fantastic.