Arriving at the right database design is the critical success factor for any successful application software development. Since it is at the start of the project, very often we are in a hurry to show some progress hence in a hurry to finish off the design. Spend enough and more time for design, it is an investment!. If the design is good then half the job is done. If the design is bad, the work involved gets doubled. Keep designing, till it gets simple (near third normalization). Sometimes there can be situations where everyone involved agrees on a particular design and you are not completely convinced. Dont force a decision. Stop the discussion, get into some other activity, then get back into the decision making process again.
The gurus have already spreading word on evolutionary design and data base refactoring (www.martinfowler.com)