I still recommend reading travel guides as an insight to a traveller's perspective on fantasy worlds. Nearly all characters end up travelling at some point, and they have many of the same needs and concerns covered in travel guides.

The Black Magician Trilogy' was about a conflict between countries and was very limited and almost claustrophobic in its range of settings, while 'The Age of the Five' was about a conflict between continents.

The first rule of world-building is available physics, which basically means that if you want it to feel real, it has to follow the same rules as this world, from gravity to how human behaviour works. If you have a fantasy element that doesn't obey the laws of physics, make sure that it has a fantasy explanation.

I always love writing the third book in a series because you get to tie up all the threads that you put out in the first two books. You finally let people know what really happens and reveal all the secrets and bring certain characters together.