The Aerowinx 747 PC sim is a pretty good systems trainer, and it comes with a manual which will give you a good technical grounding.
There is a book called ace your 744 sim check or something, by an ex United guy - Its OK but its very expensive and is mostly taken up with cockpit flows and general operating practices which are usually company specific and best taught by the trainers I think. There are some quite good tips in it though.