Everyone wants tender meat with great flavor. So what makes the difference? It is a lot of things coming together at the same time.
You need to start with great genetics from beef breed to produce a superior animal. They need to be able to eat so they can gain and put on weight. The age that you process the animal is also very important. Usually 18-24 months of age. If you process earlier the flavor may not be what it should be and it you wait to long the meat may be tuff. There is most certainly more to it then that but that is the quick version.
I believe the single most important thing other than what is listed above is the dry ageing of the meat with your processor. (how long you hang the meat in the cooler before cutting it up.) You can research this for hours and find a ton of answers as to what the best time to hang you beef from one week to over 100 days. but most commonly the answer is 14-21 days at 35-38 degrees. There is also many other factors going on during the dry ageing process. but with out going into everything, the one take away you should get from this is Dry ageing beef is it makes it tender and you should ask your the butcher about it.
One of the ways you know a beef is ready and will have enough fat to be tender is the fat between the front legs at the brisket. it should be full like the ones below