One thing I've noticed is that some people who want to learn English become obsessed with sounding like a native speaker. Not only is their main goal the sound of their voice rather than their comprehension and communication ability, its often unrealistic.
Some people believe they can sound just like a native speaker in a very short amount of time. I know foreigners who have lived in Canada for years who do not sound like a "native speaker". You can immediately tell when they speak that they are from another country. However I can also completely understand them and have no problems speaking to them.
You can try for a very long time to sound like you were born in North America but unless you were born here or moved here at a very early age (many studies suggest that anyone moving here over 15 years old will always have some accent) it will be extremely difficult, expensive and time consuming. I suppose that it would be possible through some advanced speech therapy to completely remove your accent, but unless you are having serious communication issues because of it, why bother?
Ask your self these questions:
1)Do people often ask me to repeat myself?
2)Do I get improper answers to questions I ask?
If you answer yes to those, your pronunciation may need some work. If you answer no, chances are your pronunciation is just fine and focus on vocabulary and idiom building, don't worry about sounding like the average Joe in North America.
I also want to work professionally using this language, so I suppose it would just help me to sort of try and remove some of my English/Spanish accent when I speak. That's just me though.