Rub it with kiwi fruit.

Buy a meat tenderizer and whack the heck out of both sides of the raw meat before cooking. Works wonders on tough chicken breast.

If you are making a beef stew or something with beef mince, put into the gravy or sauce mix a few drops of Worcestershire sauce (Lea and Perrins type) this really does work and makes the gravy taste richer.

I had a piece of pork one time and I sprinkled it with meat tenderizer ( in the spice isle of store) and left it in the refrigerator overnite. The next day I cooked it in my pressure cooker at the recommended time and it was the most tender pork I ever had.