I didn't use a book - I played it by ear! Essentially you can start with whatever food you like, but you are best to keep to things that are generally well-tolerated by most los to reduce the risk of reaction. Sweet potato is a good one to introduce early on, as is carrot. Fruits I would suggest are pear or apple. Everything should be well-cooked. If you are doing blw, then you should cut it into shapes that are easy to hold, if you are doing purees then you should make them pretty smooth to start with.
In general, it is advised that you start introducing foods in the middle of the day so that if there is a reaction your lo might get over it before bedtime. It's also a good time in terms of lo being fairly receptive as they will not be overly tired. It is also generally held that you should only introduce one food every 2-3 days, again to watch for reactions, but I never worried about that too much - if you don't have a history of allergies in the family then you probably don't need to observe it if you don't want to. However, one sweet potato goes a very long way with a 6mo, so you might find yourself giving one thing for 2-3 days anyway!