The English alphabet is a scam!
I say so because it is non-phonetic meaning the letters will trick you- they will be spelt in another way than you might think. For example take the word about. Instead of əˈbaʊt (UH-BOUT) learners are likely to say æbaʊt (AH-BOUT).
So there is a very subtle difference in tongue movement (we are talking about a matter of millimeters). This will make the difference between giving the impression your English is not so proficient and being accepted as a native speaker! So, here is the secret weapon for perfecting your English accent: Enter, vowel chart!
The vowel chart is a cross-section of the inside of your mouth. It will help you to become mindful of tongue movement. Where is your tongue when you say the vowel sound in cheese (IPA symbol of EE is i:)
The tip of your tongue reaches close to the alveolar ridge, a few millimeters before your upper teeth.
Matter of millimeters
How about when you say the vowel sound in moon *(IPA symbol of OO is u:)? The back of the tongue gets bunched and moves back into the mouth, upwards.
You can remember the tongue goes up for the vowel sound i: (cheese, please, seed) with this phrase: reaching for the cheese.
In addition, you can close your eyes and really get mindful of tongue movement. Try say i: + u: (chEESE, mOOn) and feel the tongue shift back and forth.
Get even more mindful of your tongue generating the u: sound by being conscious of how the sides of the back tongue touches the inner molar teeth- very delicate, but I’m telling you these are the sensibilities that must be considered for a flawless accent.
Difficulties for Asian students
Sometimes my Asian and European students have difficulty differentiating between a long vowel and short vowel sound. They would say: spickers instead of speakers. The vowel chart makes you realised, you have to move your tongue tip up ever so slightly, a few millimeters- then the air for lungs can take a ride on your elevate tongue for you to successfully pronounce a long vowel EA sound.