Stir fry is a quick way of cooking veges, on high flame. For the various veges to cook evenly, cut them all to same bite size.
Veges like broccoli and carrot needs to be blanched for about 3-4 minutes before adding to the pan, for all to cook evenly, the same goes for any other hard veges- blanch.
In case you're using meat/ fish or for vegetarians- tofu, cut them into bite size for even and thorough cooking.
In the pan, food needs to be stirred often to prevent it getting burnt.
To add flavour to your food, you can spring onion greens last, a dash of lime juice, once you take dish off the fire, roasted sesame seeds, coriander leaves finely chopped.