Lesson #3 : Visit the site frequently - at least every other day. Many details will be missed if you only see the final product. On each visit, review the work done and do not be afraid to ask questions. Some silly questions have major consequences.
Example : we noticed that the newly tiled floor was level with the entrance. The contractor had raised the floors of the toilets and kitchen without consulting us. This means if we splash water to wash the toilet/kitchen, it will flow into the next room! We had to call a site meeting to try and work around the issue. Of the problem was caused by initially by our failure to be specific about what we wanted (next lesson).