Make sure your camera settings are correctly configured for taking action shots.
Set your shooting mode to continuous, so that you can hold down the shutter button to take multiple images with your cameras burst mode. Set your burst speed to the fastest possible, which will enable you to take the most amounts of images in the least possible time.
Set your auto focus mode to AI Servo AF. AI Servo AF will let you lock focus on your target and then continue to focus as the subject moves toward or away from the camera while depressing the shutter button half-way.
Set your dial to AV (aperture priority). Setting your camera to AV mode will help ensure that you have enough depth of field to keep the whole bird in focus.
Set your aperture to f/8. An aperture of f/8 is a good balance between getting the entire subject in focus and maintaining a fast enough shutter speed on a sunny day. An aperture of f/8 is also the sharpest setting for most lenses and makes a good starting point. You may, however, want to shoot wide open on cloudy days or if the background is dark.
Set your ISO to as high as necessary to achieve a shutter speed of at least 1/1000s. Generally youll want to freeze the bird in flight and youll probably be handholding the camera and lens, so a shutter speed of 1/1000s makes a good compromise.
Set your cameras auto focus selection point (AF point) to the center AF point only. By using the center AF point only, you will more likely be able to keep the focus on the moving bird rather than having it lock to the changing background as you pan across your view. The center AF point tends to be the most sensitive of all your cameras focus points.
If your camera has built in Image Stabilization (IS) youll want to turn it off. Image Stabilization (IS) is a feature that helps the user take pictures in low light with slow shutter speeds. At a shutter speeds above 1/500s, IS only serves to slow down the cameras autofocus speed. Most people think that the best setting is to leave the image stabilizer on and to set it to panning mode. However the image stabilizer slows down the auto focus system, and faster auto focus is more important than image stabilization, especially at shutter speeds of 1/500s and faster.
Your lens will require some configuration as well, if you are to get the most out of its performance:
Make sure that your AF/MF switch is set to AF (auto focus). You wont be able to take many shots of birds in flight in the MF (manual focus) setting.
Set the minimum focus distance on the lens to its furthest setting. By limiting the focus distance of the lens, your auto focus will lock on target much faster and will be less prone to hunting for the target. Since the birds will be flying perpendicular to your lens, you shouldnt need to worry too much about birds flying closer than the minimum focusing distance of the furthest setting.
Hope that helps.