To Increase Knowledge

I have found that the internet and sites like this one with its article section to be more use than books. Some of the books I have read have been worse than useless in their advice. Click on 'Fish Articles' in the menu bar at the top and have a reading session. For fish themselves, look at the 'Fish Profile' section or this website.
Magazines such as Practical Fishkeeping are a better source of info than books, though you may not be interested in any of the articles in some issues.

Not sure if you use a smartphone, but I found a very hand app which I think is called Tropical Fish Advisor. It costs 1.99, but has lots of info on fish and plants along with some useful calculators. A very handy app when you spot a fish you fancy and would like to know its requirements (tank size, pH, hardness, etc.) as well as common illnesses. It also has a great advanced search feature for narrowing down which fish are suitable for your tank.