There's a branch of linguistics called "applied linguistics". Within it the people studying it learn how to - and this part is crucial - teach a person of a given nationality a foreign language of choice using proven, mostly effective methods. As you see, the AL process is going to look like differently for an Italian leaning Spanish and an American learning Polish. This is why the person that can guide you, a teacher, must be of your native nationality. It takes on average 2,5-3,5 years of not that hard work to make a person speaking let's say English into someone who's impossible to distinguish from native speakers. I've seen the results myself, and I was glazing my eyes!
Instead of looking for a regular teacher take the one that's been studying applied linguistics instead. Those people aren't much more expensive. You need a guidance of that kind because someone knowledgeable must tell you what you, specifically, do wrong. Having that knowledge and reasonable tools to address your challenges you're going to love what you can get from the learning process.
I'm the best example :) My teacher told me after 2 years that I'm the most untalented, lazy, not motivated enough, stubborn person she's ever seen in her life. Plus that the fact that she made me who I am today is her greatest success ;) Kudos to her - I'm doing pretty fine with English (being Polish). Moreover, I know what I don't know, so now I can work on my own. You can't put a price on that.
Good luck!