Overblowing, or cranking, is simple. It is easiest to do on a conical bore instrument. These include trumpet, trombone, French horn, and tuba. You may experience more difficulty trying to crank on an instrument like a cornet or baritone, but a practiced performer can achieve the desired sound.
Let's start with the most important step: a huge breath! Open your mouth (think "aah") and let the air come in. Do not force yourself to take an audible breath. You will need as much air as you can because you will be using all of it for almost every note you play. Be sure to breathe often, up to between every note.
It's okay to puff out your cheeks. It may help keep your lips more relaxed. This brings us to step 2: PUCKER UP! Bringing your lips closer together than normal will allow the most flappiness. This lets all the air flow through easily.
Lastly, lean into each note you play with your body. This helps generate the maximum SPL (sound pressure level) to your audience, which gives them enjoyment. It will also give a visual dictation of where each note happens, helping your audience understand the music better.
Now you know all you need to crank. Go out there and have some fun!
In the next lesson, we will explore pedals!