Add the coursely chopped fat, whatever fat you have, to either a cast iron pot or a heavy-bottomed cook pot. A cheap, thin-bottomed pot will likely burn the fat.
Add water up to about 30% to 50% of the top of the fat.
Turn heat on high until water begins to simmer/low boil. Reduce heat so the water just simmers. This will get the rendering started without burning anything. Now go away and read a book or paint a picture or whatever.
Occasionally look in the pot. When the water is gone, or almost gone, reduce heat just so some bubbles are still being produced. Go back to book.
Look at pot. If water is gone and melted fat is being produced adjust heat so a cooking thermometer shows a temperature of 180F. As more fat is produced reduce temperature to 160F.
As long as there is enough heat to cause the trimmings to bubble, rather like bacon in deep fat, then fat is being rendered.
As the end draws nigh, the fat and meat particles will be turning brown. Remove from heat and using a slotted spoon remove all the trimmings you can. If the trimmings continue to cook, they will burn and the fat will taste burned. DO NOT LET THE TRIMMINGS GET TOO BROWN. THE MORE BROWN THE TRIMMINGS, THE DARKER THE RENDERED FAT. IF THE TRIMMINGS ARE TOO BROWN, THE RENDERED FAT WILL TASTE OF OVERCOOKED MEAT. If you remove the trimmings before they turn brown, the renderings will be clear when melted and white when cool. Browned trimmings will add a golden color and a light flavor to the renderings. The browner the trimmings the more golden the color and heavier the cooked meat flavor.
My renderings are a light golden color and lightly smell of browned meat. Back when I was eating biscuits and gravy, this fat with the very light flavor of cooked meat gave the biscuits and gravy a background flavor that was unbeatable.
Allow to cool, pour into a storage container, tightly cap it, and store in a cool spot. There may be a bit of water in the bottom of the pan if you have not completely cooked it off. Be sure none of it gets into the storage container.
After 24 hours look at it and if any moisture is on the surface of the hardened fat, wipe it up with paper towel.
This may read as complicated but it's not. Just use the minimum amount of heat to get the job done and keep an eye on the process. My grandmother used to render the fat from several hogs at a time. She would start the process then move to other chores while the lard rendered. It ain't no big deal. Just be patient, sez Granny.