Some common mistakes when making green chili are over seasoning with tomatoes, not browning the pork or beef first, boiling the meat instead of braising the meat, burnt or raw flour, relying on and using canned chiles and leaving the skin and seeds on.
Traditional green chili is distinct in being pepper forward.
And adding too many crushed tomatoes or tomatillos to the green chili can overpower the delicate and earthy flavor of the green chiles and push the green chili dish too close to a marinara or red salsa instead of green chili.
And dumping the raw meat directly into the pot of liquid also means that you miss out on the deep, caramelized savory flavors, and so you should always sear the meat cubes in some oil first to buildup a solid base for the green chili.
And whether you're using beef or pork shoulder, rapid boiling of the meat instead of braising the meat will result in the meat being tough and dry.
The meat for a good green chili needs to cook low and slow in the braising liquid so that it breaks down and becomes incredibly tender and infuses the green chili with it's rich flavor.
And many recipes for green chili also require a roux made of flour and fat to thicken the green chili.
If you add the flour directly to the bubbling hot liquid, it will clump up.
And if you cook the flour at too high of a temperature, it will also burn and give the chili an acrid, bitter taste.
You should toast the flour gently alongside your aromatics, like onions and garlic before adding any liquid.
And while canned green chiles can be used in making green chili, it's best to use fresh roasted green chiles like authentic Hatch chiles when in season or fresh jalapenos or poblanos as canned green chiles can be mushy and overly vinegary.
And not peeling the peppers leaves a tough, bitter texture from the charred skin and leaving the seeds, ribs and veins in the green chilies can also make the green chili overwhelmingly and uncontrollably spicy.