When your stir frying, the key is to cook the meat and vegetables quickly over high heat. If you add the meat to the pan first and then start cooking the vegetables, they can become overcooked and soggy while the meat remains tough.Frying your meat before stir frying in a pan is way better. Mixing it with cornflour will help to seal in the juices and keep the meat tender.
Using what you have in the fridge is always a great way to come up with a quick and easy meal. You can either fry some beef or chicken up, or use some leftovers from a previous meal. You can use whatever vegetables you have in the fridge, just make sure they're chopped up into small pieces so they cook quickly.
Use whatever seasonings you like, but as a base its good to start with soy sauce, oyster and sugar.