There are few non technical things in this field which are more important than the technical parts. Lets discuss that first.
Non-Technical / Behaviourial Knowledge
#1 To me, the thumb rule of bird photography is love them first. If you dont love them how will you enjoy those moments spent behind these beauties?
#2 Second important thing is patience. Phtographing birds is not like a studio setup. When I started bird photography I always found myself standing in field with my camera without any bird arounds. Most of the time I was disappointed that no birds available for shooting. Slowly I understood this is not as easy as I was thinking. Birds are always very alert. When they will see you appaching towards them they will fly away. So, be patient. Whenever you see a bird approach towards it very slowly. If you see the bird noticed you and in a alert position, stop there wait for some time. Always make a move without the knowledge of the bird. The best thing if you can use some tree, bushes or rock as an hide. I know few well known wild-life photograhers who use hide to shoot birds. They wait for a whole day inside the hide in a hope the bird will perch near by. If you are lucky the bird will perch there or you have to try next day again. I have also seen Indian birds are well accustomed with car than the human beings. And I got many time success to shoot a bird from a car.
#3 Thirdly, you have to know the Bird's behaviour and habitat. It's very important to find a bird in its natural habitat and shoot them. As an example you can not expect a Kingfisher in a dry hill region. If you know how Kingfisher perch you can easily find them around a water body. If you know an owl's behaviour and habitat you can find them easily. The best time to photograph them is late afternoon as they are nocturnal birds and become active from late afternoon. You can photograph them in day time also if you know their habitat well where they spend their day time.
#4 Fourthly it is important to know the breeding period of a specific species. In this time you can have beautiful picture of both sex, courtship etc. And this is the time when the activity of the birds are always high. Not only that few birds get a special breeding plumage to impress their opposite sex in this period and they are always beautiful to shoot an image. The below picture is an example of the courtship of Cattle Egret in their Breeding Plumage.
#5 The fifth important thing is your attire and your behaviour in the field. A red or yellow shirt is not advisable in field while you are shooting a bird or any wild life. You should have a green color shirt which make you camouflage in the nature. You should not speak loud. If you are in group while shooting use whistle to call your friend or take his attention. When you are in hide you have to be silent and motionless. it's also good if you use some leaves or branches to hide your hide from the strong eye of the birds.
#6 Besides the above mentioned points the over all important thing is your luck. From my experience I have returned home so many days after spending 4/5 long hours with out a good shot. You dont know what nature preserves for you. I found one day myself extremely lucky after getting the below shot at Thubarahalli Lake. I don't know if I try my whole life I'll get a shot like this or not.
#6 Timing is an another important factor here. Morning and afternoon is always considered the best time for bird photography as you can find the best activity of the birds in this periods. You will hardly find any bird sitting on a open perch under the mid-day sun.
#1 Camera - A proper SLR camera is always advisibale though I have seen people taking good bird shot with point and shoot camera with good zoom range. But in a SLR camera you will have more option than a point and shoot body.
#2 Lens - This is the most important thing in Bird Photography. As long lens you will have as you will get the reach to a particular bird. If you have a 500mm lens you will get the bird from larger distance than a 300mm lens which means you will have always an oppurtunity to shoot a bird from a distance. Canon, Nikon and all other brand have their own 500, 600 even 800mm lens specially for bird photography. Teleconverter are also being used with the combination of different lenses to get a better reach. Although it is said that 500 mm is a decent lens for bird photography I use a 400mm prime lens, even I used 70-300 zoom also and got good result from it. A zoom is always useful if you shoot any mammals when you are shooting a bird inside a jungle. The below images came only from a 70-300 zoom lens.
#3 Tripod - To me this is a very useful equipment to get a shake free image. I use tripod even in good light also to avoid the minimum shake. Now days IS (Image Stabilization) lenses are available in the market but still tripod or monopd gives a cmplete shakefree image.
#4 Others - Besides these three basic equipments there are lots of other equipments available in the market to get better bird image. Example - Hide, Light Meter, Flash etc.
#1 Focus - This is the most important thing while shooting anything. Bird photography is not an exception. You have to ensure that the bird is in sharp focus from head to tail. In the below example the Scally Breasted Munia is in full focus. That's the reason the image came sharp with full details of the bird.
#2 Natural Perch - It is always preferable to have a natural perch in Bird Photography. While I was shooting the scally Breasted Munias I have seen them percing in eletric wire. But I waited for them to come down on a natural perch.
#3 Eye Level Shot - The bird should be at eye level when you are shooting. In the Munia shot I folded my tripod to the smallest fold and sat on the ground to get this eye level shot.
#4 Lighting - The lighting is always important and catchlight on bird is always preferable. Remember the sun should be at your back and on the bird while shooting. If you find a bird opposite to the light try to move in opposite direction whenever it is possible.
#5 Background - A clear background frame a bird image. A smooth background is always preferable in a bird image rather than a noisy or busy background. The River Tern in the below image stands out in clear green background.
#6 Position of the Bird - This is equally important while you are shooting a bird. If the face of the bird is opposite to you wait for the right time when the bird will turn towards you and then press your shutter.
Besides these there are so many small points which one can acheive slowly slowly with his experience. Every body has his own style of shooting and they develop their style and strategy with experiences. Lastly it is the joy what a true nature lover can acheive after observing and capturing a bird and share the same with others. It's not only important to capture a good image of a beautiful bird, but also understand it's importance in nature. At the same time it's important to share the same to others to save these species for long time.