Many sounds in English sound almost exactly the same in everyday conversation. Growing up in the U.S. we imitate our parents in how we shape our mouths to produce unique sounds. Actively engaging your cheeks, lips, tongue, and jaw will immediately improve your pronunciation. A lot of adults who learn English as a Second Language (ESL), have trouble mobilizing and coordinating their faces with the sounds they are speaking. Some hardly move their lips at all, as it they were paralyzed. Others try to talk so fast their mouths cannot keep up with their thoughts.
Lip readers can understand spoken language without hearing it because each sound has a unique facial configuration. That means that the meaning of the words is contained in the facial shapes. Because they are activated my muscles, the mouth parts acquire muscle memory they call upon whenever they need to make a specific sound. If you try to intellectually remember the sound, results are much poorer.
Say "P" pork. Your lips should be completely closed. Your tongue is in the middle of your mouth. You puff out your cheek a little bit, then release your lips in a small explosion- P. Now say "F" as in fork. Now, though the other parts of your mouth are just like "P", your lips are not closed tightly against each other. Instead, your upper lip is pulled back, while your lower lip presses up against your teeth. Instead of the explosive "P" sound, the breath gradually escapes through the teeth to make an "F" sound.
Try some exercises for your mouth-- mouth yoga! Puff out your cheeks, makes faces like a little child, open your mouth as wide as you can, move your jaw side to side. Do this for a few minutes, and when you stop you can feel the blood tingling in your lips. As you practice you will become more aware of how your mouth and face is arranged. Many sounds require changing the shape of your face and mouth to produce. Others remain constant. What shapes are the hardest for you? What sounds are the hardest?