I write up a schema, send to everyone else on the team, get feedback. If users are invovled get it from them too.... take in all the feedback, write up a new draft, wash, rinse, repeat until running out of shampoo (i.e. feedback).....

Once things are pretty stable, do a prototype, address any oversights, do the real thing.

It's not rocket science.

That doesn't mean spending months planning. It does mean doing your best to plan over a few days, then prototype, review, and start implementing. If things change, you now have a clearer idea of the issues and can better address them.

The worst thing you can do is go into development both blind and without important tools you need to make sure that requirements are met--- tools like check constraints, referential integrity, and the like.

large changes? throw away and start over; tools like Rails can help you get up and running really quickly.

I rarely see people go back and fix the mess.