Nothing is worse than a tough steak. You'll chew and chew for hours without getting anywhere. There are several ways to tenderize your meat and make it so soft it will melt in your mouth. It will work for making soups, steaks and any other type of beef dish.
The actual meat is very important. If you buy a cheap cut of meat, you will likely suffer the consequences by chewing on the beef for hours. Buy a quality cut of meat, such as the filet, the rib eye or the sirloin, for best results.
Preparation options: Hit the beef with a meat mallet (aka steak hammer) thoroughly. If you don't have a meat mallet, use a meat tenderizer to poke holes into the cut of meat. This is the best option if you are going to use a marinade. Not only will it make the beef tender, it will let the marinade sink in and give flavor to the entire piece of beef.
Cooking hints: If possible, cook the beef using a slow cooker or crock pot. If you don't have either of those, or you are going to cook it in a different way, make sure not to cook the meat on high heat (375 degrees F or higher) for a long time. This will dry out and toughen the meat. It might be OK if you have tenderized the meat already. Use a marinade to give the meat more flavor and keep the meat juicier without drying it out.
For final touches, don't eat the meat immediately. Wait 5 minutes to let the meat rest before serving and eating. If you haven't overcooked and dried the meat out, the beef can simmer in its own juices or the marinade for a few extra minutes to soak it up before you eat it.