When buying steaks, buy the best grade of meat you can afford. It should be USDA Prime Aged Beef. If your butcher does not have this, the next best grade is USDA Choice.
Look for steak with fine texture and firm to the touch. You want the color to be a light cherry red color (not deep red).
Also look for steaks that have marbling. as it is the thin threads of fat running through the meat that make it Prime and gives the wonderful flavor. Marbling is the white fat that you see in all cuts of beef. Remember that a substantial amount of evenly distributed marbling is a good thing. Look for small, evenly distributed specks of fat rather than larger and sparser ones.
Marbling is the fine specks of fat within the meat. While studies show that marbling does not significantly increase the caloric count of beef, it greatly enhances flavor and tenderness. Beef that's richly marbled gets a higher grade; it's more tender, juicy, and flavorful because the intramuscular fat melts and bastes the flesh during cooking. Also, since fat insulates, marbling provides some insurance against overcooking. If you don't want much animal fat in your diet, then don't eat steak! To avoid fat in steak is to avoid steak altogether.
Size or thickness matters when purchasing steaks. The best steaks are 1-inch to 1 1/2-inches thick. A thin cut is likely to get dried out. The thickness of the steak is more important than the weight.