Warm-up by picking a major scale and doing the basic solfege warm-up (singing the major scale in solfege symbols, with hand gestures). This will get your voice prepped to do larger intervals.
Sing the first note, which is Do, and hold it out as you make a fist at your midsection.
Repeat that note (Do) and make the fist, then go a second interval up (one whole step) to Re, then back down to Do. The hand sign for Re is your hand at a 45-degree angle upward, fingers together, palm down. Therefore, you should be singing "Do-Re-Do" while your hand goes "fist, angle up, fist."
Sing Do again, and then move a third interval (two whole steps) up the scale to Mi. The hand sign for Mi is with your hand flat, parallel to the floor, palm down. Your voice will sing "Do-Mi-Do" while your hand makes a fist, goes flat parallel to the floor and then makes another fist.
Recap Do again, and then move your voice up a fourth (two and a half steps from Do) to the syllable Fa. The hand sign for Fa is the thumbs-down gesture. Your voice will sing "Do-Fa-Do" while your hand moves from fist to thumb down back to fist.
Begin with the Do syllable once again, and then sing up a fifth interval (three and a half steps) to So, and then repeat Do again. The hand sign for So is your palm flat/parallel to your body. As your voice sings, "Do-So-Do" your hands will move from a fist to a flat hand parallel to your chest, back to a fist.
Go back to your starting point again, which is Do. This time your voice will do a sixth interval (four and a half steps up the major scale) to La. The hand makes an upside down C when signing La. You will sing "Do-La-Do" as your hand goes from a fist to an upside down C back to a closed fist.
Sing Do again, and this time skip up a seventh interval (five and a half steps) to the solfege syllable Ti. The hand sign for Ti is a pointer finger, pointed up at a 45-degree angle. You hand will move from a fist, to pointing up at a 45-degree angle, back to a fist as you sing "Do-Ti-Do."
Repeat the low Do syllable one more time. This time you are going to skip to an eighth interval, also known as an octave, all the way to the high Do. An octave is 6 whole steps. The hand sign remains the same (a fist), just at a different place on your body. So, as you sing Do-(high)Do-Do, your hand will stay closed in a fist and just move from waist level to eye level and then back to waist.