Asian cook here... I make stir-fry alot and find that a good pan makes all the difference. I use either a cast iron pan or, my favorite is a 14" stainless steel chef's pan. It's thick on the bottom and has a domed lid. I used to use a non-stick pan but that didn't worked well because you can't heat it hot enough.
The trick to the stainless steel pan is to heat it first, medium high heat til hot, then add the oil, tip the pan to cover the bottom, wait a few seconds for the oil to heat and throw the meat in right away. If you do that, the meat shouldn't stick to the pan.
The meat has to be sliced very thin so it cooks quickly. Remove it from the pan as soon as it is cooked. You have to cook in small batches or it all sits in the pan too long and gets tough. You may have to divide the beef strips and cook one part at a time and keep it warm in the oven while you cook the rest. But it shouldn't take too long if the strips are thin and the pan is hot. What takes longer is the prep, to make sure the strips are thin and even.
Another way to get tender beef strips is to saute quickly, then add liquid, cover and simmer. If I have vegies, I like to saute them separately first, then add them back to the pan to simmer with the meat. If I'm in a hurry or feeling lazy, I just throw the raw vegies in with the simmering meat.
Here's another thing to try. Dredge the beef strips in flour or cornstarch before frying in oil. The coating will brown and the meat will stay tender inside. Fry quickly then add beef broth. The flour/starch will simmer with the broth and make a nice gravy.
By the way, you have to use oil! The traditional way to make stir fry was with pork fat or lard. But you can use canola or vegetable oil to make a heart-healthy dish.