One thing I learned with my speech pathologist when I was young was when practicing to say words like "the" or "three", you should put your tongue gently between your teeth and then say the word, it should sound much more clear and help with pronunciation. I think this can be used with any "Th-" word and overtime it becomes a second nature to where you do it without noticing. For words like "to" I would try and get better at saying words like "Choo" and "Two." It gives this sound that is all similar and should be a starter for getting better at producing it more clearly. For other words and speaking, if you start producing weird sounds and saying words differently, then I would suggest pausing and recollecting yourself then continuing at that normal pace. I honestly don't know if this is helpful advice haha but I hope it helps to some degree. Good luck!