I believe that the best way to improve your pronunciation - whilst continuing to learn at the same time - is to immerse yourself in the language. Read English texts. Watch English Films and T.V. You could passively listen to English podcasts or the BBC World Service whilst driving or doing chores. You will find that there comes a point when you stop translating in your head and actually start to think in English. Perhaps that is the time when you would gain the most from engaging with a native English speaker to hone your accent. You have a positive attitude Maria, it will take you far.

I'm not a native speaker and I certainly don't pronounce like one, but one thing I do sometimes is listen to people in conversations or interviews and try to emulate this person's pronunciation. It's not easy or very interesting but eventually I find some small corrections in words or the way I move my mouth when I say them. I think this can be helpful specially for words that are unusual or difficult.

Thanks a lot!

I believe the best way is by speaking with a native speaker and carefully paying attention to your diction and the sounds of letters. I know that even native speakers use diction CDs and carefully repeat each word until their accents fade :)