What is the main religion of your world?
Main can be either the most powerful one or the most popular one.
Worship who or what?
(go to #28 Holidays for questions about that)
Are there foods that are not to be eaten because of the religion? (related to #16 Food)
Are there certain ways to dress because of the religion? (related to #14 Fashion)
Are there laws influenced by the religion? Does the government have a say in those religion influenced laws? For or against it? Perhaps, in conflict with the religion? (related to #8 Government)
Religion is another one of those like the climate which can affect many aspects of your races/species lives. Food, fashion, language, education, government body itself, governing laws, holidays, recipes...the list goes on and on. Oh, housing styles, too.
Religion is a very powerful element in fictional worlds. If it is the center of your world, recall our own Earth here and how religion has affected many people's lives.