There are four important things to think about when trying to help and ill or an injured bird.
1. Heat
2. Hydration
3. Nutrition
4. Noise and activity level
Heat
Birds use a huge amount of their energy to keep up their body temperature, which means the most important thing you can do for your sick bird is to support this tempurature to help the bird preserve energy. Too hot is bad, so if the bird starts to pant reduce the heat. As your bird gets better, gradually reduce the temperature back to room temp.
Hydration
Keep your ill bird hydrated is a key element in nursing your bird back to health. The bird may not be getting the fluids it needs due to the it's illness or injury. It could be struggling because of a high temperature or a disrupted digestion. It is important to help your bird get the fluids if it is lacking them. This can be done by giving fluids from a spoon or by syringe. Apple or grape juice and water with a little sugar or honey are good fluids to help your bird, as well as just normal clean water.
Nutrition
The bird needs as much energy as possible to help fight the illness, and needs plenty of easy access to nutritious things just as infant rice cereal, baby food, ground up pellets mixed with fruit juice (not any citric-y juices though). In some causes it is necessary to hand/force feed your ill bird, as to stop it from staving. If the bird regurgitates food or fluids, you may be giving it too much. Smaller amounts more frequently is better.
Noise and activity level
The ill bird should be kept in quiet and in semi-darkness to help it get as much sleep as possible. There should be no toys for the bird to waste valuable energy on either.
> Even if your bird is acting normal again and seems to have fully recovered, don't stop supporting it too soon. Check that it is drinking and eating enough, and that it is warm enough. > If you have a bird with a breathing difficulty, then humidity is greatly important, as it helps the bird keep its air passages clear and moist. Wheezy, rasping clicking noise made when breathing, heavy breathing, open beak to breathe or moving tail as the bird breaths are signs that the bird is having trouble breathing.
PLEASE NOTE: The help above is only while you are waiting to get the bird to an avian vet. These actions alone are not likely to cure your bird and are not instead of the help of a vet. Please keep that in mind.