Firstly, you can only include improvements to real property. Real property is land plus any permanently attached structures (including landscaping). So furniture and appliances are right out from start.
Then, improvements add value or extend the useful life of the home or its sub-systems, while repairs keep the property in as-was condition. Repairs are the responsibility of every homeowner and there are no tax breaks, they don't add value or extend the useful life of the property. (However, if you remodel the kitchen or add an addition, the entire cost would be considered an improvement and you don't have to subtract the cost of painting that is part of the overall job.)
Windows and flooring would usually be seen as improvements that add value or extend the useful life of the home. Lights, maybe yes or no, depending. Built-in appliances may count if they are permanently attached to the home, but most appliances don't count, nor does furniture or painting for general freshening-up.
