I'm not sure how much of the fat to leave on the meat before I grind whether it be chicken, beef or Turkey
What's the best method for grinding chicken vs beef vs Turkey, etc.
That depends on what consistency you like, how oily/fatty you like your food, and the kind of food you are preparing.
For things cooked on high heat, like hamburgers, more fat will give the meat more flavor and tenderness.
For things cooked on lower heat, like spaghetti sauce or a casserole, less fat is generally preferable as the looser ground meat will absorb more of the flavor from the sauce/seasoning. It will also make the dish more attractive by not having a layer of oil from the fat floating on it.
Always promptly and carefully wash the grinder with hot water and soap after using. Ground meat is more vulnerable to bacteria due to more surface being exposed to the environment.
It is a good practice to sanitize the areas of the grinder exposed to the meat after, and even before using it. You can purchase food-grade sanitizing liquid online or from a restaurant supply store. This is especially important dealing with poultry meat. Poultry, especially ground, is particularly vulnerable to Salmonella. Here is information about handling poultry from the CDC.
Use mineral oil to lubricate the grinder plates, knives and corkscrew regularly. You can also use it on other steel surfaces to preserve its appearance.
Grind meat twice to get a smoother appearance and texture. Some types of recipes may call for just a coarse grind but generally you will prefer the smoother kind.
Mix types of meats together for interesting results. For example, Bolognese style pasta often using a mix of veal/beef, pork and lamb.
Add your dry seasoning to the meat before grinding to make it more even and quicker to prepare. This works great for things like meatloaf, sausages, etc.
Accessorize! You can usually purchase things like sausage tips so you can make your own. If you have a dehydrator you can make jerky and meat "sticks" (like you can buy at the gas stations).