I tend to validate my design by collecting a list of questions the database has to answer. If I can work through how to design the queries (not necessarily do it, but which entities are involved), then I know I'm on the right track. If I"m not sure, I will add a few records to the tables I need to answer a question and see if I can write a query that will return the expected result. Definitely start with as few records as you can - you can delete them all later before loading the real data.

Not incredibly technical, but it works.