- Read widely, non-fiction as well as fiction. Ideas for world building can come from finding out how things work, how scientific discoveries and so on were made. That tip came from Terry Pratchett in an interview many moons ago and I've found it really helpful. One of my non-fiction books looks at the role of people in the palaces and how those roles have changed over the century. Very useful for working out how I want to "staff" my Fairy Queen's Palace. I took the basic ideas and then embellished them for my own use. This can be done with almost any non-fiction book. Work out what you need and read up on your subject matter.
- Be realistic. Sure, in a fantasy world magic is going to play a massive role in things, but if everyone has the same level of powers/skills there will be no conflict (and so no story). So different people must have differing powers/skills and the conflict comes from when people want more than what they have and are prepared to do anything to get more. Or when others want to suppress people developing their skills and so on.
- What happens when things go wrong? Think about how your world is governed (globally, nationally, locally or any combination) and ask what would happen if the system of government broke down. Also what happens when magic goes wrong? Who fixes the damage? Can they fix the damage? What are the implications for the environment?
Hope you find these thoughts useful. But reading well always pays off. Depth of knowledge comes through in a story. (Not by showing off, that will put readers off, but you will write with a confidence that comes from knowing your subject and that will come through).