English students can be seriously preventing themselves to become better by negative opinions that their accent is bad. First, you have to know that your accent is not bad; it is just nonstandard to the American ear. Here is a famous joke hahahaha lol:
John: What do you call a person who can speak three languages?
John: What do you call a person who can speak two languages?
John: What do you call a person who can only speak one language?
Every language is equally good, so every accent is good. The average American, however, truly does have a hard time understanding a nonstandard accent. English and Americans are two people divided by the same language. Some students learn to over pronounce English because they naturally want to say the word as it is written. Too often an English teacher may allow this, perhaps thinking that colloquial American English is unsophisticated, unrefined, or even incorrect. Not so at all! Just as you don't say the T in listen, the T in water is pronounced D, wader. Any other pronunciation will sound strange and wrong, or different to a native speaker.