Thank you so much for your question! As a pronunciation specialist, I appreciate your curiosity and your desire to pronounce "soon" correctly (as far as the American voice goes).
For the American pronunciation, you need to speak three sounds: /s/ /oo/ /n/.
First, the S-sound (/s/). With relaxed jaw and lips, the tongue moves toward the back of your teeth, while the front of it pushes down slightly.
Second, the long-U sound (/oo/). The /oo/ sound is in the word "you." If you drop the Y and say the sound that's left, you would have /oo/. (I.e., you = ou = oo.) For the /oo/ sound, your lips come together, but do not tighten (or purse) your lips too closely together; you want to be able to release air through a small opening still left open in the middle of the lips. Your tongue does two things: 1) the back part of your tongue stretches a little forward, toward the center of your mouth and up toward the roof of your mouth; 2) the front part of the tongue presses down.
Third and final, is the N-sound (/n/). The front part of your tongue needs to stretch up toward the alveolar ridge (the bump in the inside of your mouth that is right above your gum line and teeth). With the tip of your tongue pressing just below center on the alveolar ridge, your lips come apart slightly so that air can pass through the mouth.
TIP: Say each sound separately, in isolation at first. Make sure to hit all of the above steps. Then, sound out the word, connecting the individual sounds together, slowly. Finally, say the word normally BUT make sure that your tongue KEEPS MOVING from one sound to another AND that your jaw and lips are being engaged accordingly.
Hope this helps! Be sure to ask questions, if needed. I'm here to help.