Jerry, in addition to all the good advice on making sure the poly finish is smooth and cured before buffing, I would also highly suggest using some sort of microcrystalline wax. There are a number of varieties out there to choose from and they excel in preventing water spots on the finished surface. Carnuba wax works but shows fingerprints and any humidity will cause spotting. Here are a couple of examples of microcrystalline wax:

https://www.leevalley.com/en-us/shop...x?item=53Z3110

https://www.amazon.com/Renaissance-M.../dp/B001DSZWEM