I've always thought I had poor pronunciation of pretty much any language I've studied, but I always seem to do better than everyone else. My German professor was pretty impressed, anyway. She thought I had a lot more experience than I really had (which was about none).
The best advice I can give, aside from just practicing a lot, is to learn about the field of phonetics and how speech sounds are produced and used in many languages. In learning Spanish, you may not think it's useful to know how to pronounce words in another language, but it does help you get a feel for a fuller range of sounds.
Many of the mistakes you'll make when learning a foreign language are tiny things that you may not get unless you understand the physiology of speech. Things like how rounded your lips are and the shape of your tongue. In general, most of these things won't interfere with communication much, but you can still get rid of them and sound better with practice and understanding.
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"If knowledge can create problems, it is not through ignorance that we can solve them." - Isaac Asimov