I agree about a classical teacher. I had one for years who was happy to help me sing folk songs better. A good teacher will correct fundamental errors that one does not realise one is making. And one learns to pronounce words so that every letter is clear: mighty importatn with most folk song lyrics. Ask the local music department of the university nearest you where to find a teacher. I now live in a small community on the Canadian prairie and miss having a good vocal teacher. But I don't miss the city and its smog!