Native speakers of English will usually gladly help you to pronounce words that you are struggling with or answer questions you have about the American accent. This is great and you should use this opportunity. But here are some things you consider first:
1. Most native speakers are not very aware of their own language. For example you may know more about English grammar rules than they do. So, if you ask them a rule about American pronunciation, very often they have never thought about it before and they won’t really be able to help you. It’s best to write down some difficult word and just have them pronounce the words for you. You can record the words and later try to imitate the way the sound. If you ask native speakers to analyze what you are doing wrong, they will hear a mistake, but don’t expect them to teach you how to correct it. Do you really expect them to tell you something like this: “Well, you are not touching your tongue firmly enough on the gum ridge and you are releasing it too quickly.” The average person never has to think about these things and often has no knowledge about really happens in the mouth to produce sounds.
Also, native speakers usually don’t hear the “melody” of their own language. So if you are making mistakes in rhythm and melody which mainly has to do with stressing certain words and reducing others, Americans will not have the knowledge to tell you: “you should stress a noun more than an adjective” for example.
2. Also, keep in mind that native speakers are likely to “over-pronounce” words when you ask them to teach you how they sound. They might use a more exaggerated way of speaking because they have switched into their “teacher mode.” It’s funny, I have even heard people switch into a British way of speaking, thinking that this would be more helpful. Be careful about that.
So what is the solution? How should you practice?
You need to learn everything you can about the American accent by reading books on the topic. Then, you will have a good foundation and you will be able better direct your American friends when they are correcting you. You almost have to teach them what to listen for and how to correct your speech. Also, keep listening to natural American speech. Become a student of good speech. Be analytical about it.
I hope this helps.
By the way, I am now offering personal accent evaluations which will give you a diagnosis/report of your accent weaknesses and strengths and tell you which part of my accent reduction book you need to study the most. You send me an audio file of your speech. If you are interested, you can learn more on my website: accurateenglish.com