Another important thing, when it comes to learning English is, being aware of intonation. Intonation in American English is the way the voice rises and falls while you speak. Very often, it changes the main idea of what is said, going beyond the exact meaning of the words to indicate how the speaker feels. The very same sentence and the same word order, might result in quite a different idea behind your words, by only shifting the stress from one word to another.
Try reading this sentence by stressing the word in bold each time.
1. He isn't flying to Paris tomorrow.
In this case, you mean that it’s not him who is traveling but someone else. As in: “He isn't flying to Paris tomorrow. His brother is.”
2. He isn't flying to Paris tomorrow.
Here, the emphasis is on the word “isn’t” to say that, it’s not true that he is flying. As in: “Do you know that John is flying to Paris tomorrow?” “He isn’t flying to Paris tomorrow. He was intending to but he changed his mind later.”
3. He isn't flying to Paris tomorrow.
By stressing the word “flying”, we intend to say that this is not what he’s going to do but maybe something else. As in: “He isn't flying to Paris tomorrow. He is actually driving.”
4. He isn't flying to Paris tomorrow.
If you say the word “to” louder, you’re saying this is not the direction he’s flying into. As in: “He isn't flying to Paris tomorrow. He is actually flying back from Paris.”
5. He isn't flying to Paris tomorrow.
Stressing the word “Paris”, in this example, would mean that this is not the actual destination of John’s flight. As in: “He is not flying to Paris. He’s flying to New York.”
6. He isn't flying to Paris tomorrow.
Giving emphasis to the word “tomorrow” would mean that it’s not tomorrow he’s flying but another day. As in: “He isn't flying to Paris tomorrow. He said he would be flying the day after tomorrow.”
As you can see, you are saying the same words every time, just pronouncing a different word at a higher pitch. In this way, you are actually saying a different thing every time.
Why should you bother to remember this? Well, being aware of the various intonation patterns is what will make you capable of conveying the intended message. That is to say, even if you pronounce each word clearly, if your intonation is non-standard, your meaning will not be clear.
Also, in terms of comprehension, you will lose a great deal of information, if you are only listening for the actual words used. You get to understand people better, and people understand YOU better and can then focus on the point you are trying to make, rather than struggling to "decode" your pronunciation.