Re: pronunciation sometimes good sometimes bad The earlier advice from susiedqq to sing is excellent. In my experience, it helps every aspect of language learning: sounds, natural rhythm and cadence, vocabulary, fluency, comfort level, etc.
Another possibility: Watch films in English. Watch the speakers' mouths, back the film up, watch them again, repeat, repeat, repeat.
Watch yourself in a mirror while you speak. If you can, have a native speaker stand next to the mirror facing you. Repeat simple words and phrases the speaker says. Concentrate on your 'problem' sounds. Watch the speaker's mouth, then watch your mouth as you say the words. (Be sure to make this a fun, lighthearted practice! Watching your mouth in a mirror can be a little weird!)
Record your voice. Listen to how you sound. You may be surprised at what you hear. We often don't really hear ourselves, especially when we are concentrating on trying to get our meaning across.
Remember, it's not always your fault that some people can't understand you. Some people just don't have the skill to understand anything that sounds even a little different from what they are used to or expecting to hear.
I hope this helps. All best wishes,
Petra |