Photography Tips

Portraits

Use a lens legth of between 85mm and 135mm (35mm equivalent) and wider aperatures. The wider aperture will help isolate the subject by ensuring that the background is out of focus, while the longer focal length will minimise distortion of facial features making them appear more natural.

One of the most important skills is to put your subject at ease. If you are fussing around your subject will be wound up and the photo will show it. If you put some music on, make a cup of tea and have a chat then you will get a more natural photo.

Take lots of photos, tell the subject that. It means that you don't have to go for that one good shot, you can experiment and try different positions etc. Just go with the flow and move them around until you think it looks right. Some pointers.

If the man is bald, shoot from lower down and never with top lighting.
If the subject looks tense, tell them to fill their cheeks with air and blow out, this relaxes the mouth and makes them laugh.
If the subject has a large nose, tell them to look towards the camera and use a longer focal length.
If the subject starts staring, have them close their eyes and drop their chin down, wait a few seconds and ask them to look up, the stare should be gone.
If the subject has a double chin, tell them to stretch forward and shoot from slightly above head height.

Landscapes

Rainbows are among the most beautiful natural phenomena, perfect for enhancing a dramatic-lighting vista or becoming your main subject in an otherwise uninteresting scene. The best tip I found was to use a polarising filter to make: "the colors of the rainbow ... more intense and saturated. The filter operates by reducing the scattered white light reflecting off the fronts of raindrops, mist, and background, leaving the colored light of the rainbow. This increases contrast and makes the rainbow appear brighter and more colorful. Be careful not to dial in too much polarizer, though, because it can filter out the rainbow itself. Try to strike a good compromise, leaving the rainbow bright while minimizing the hazy, white light surrounding it." -from http://www.photocentric.net/rainbows_finding.htm
Use a tripod and use an aperture of f/16. Focus on an object one third of the way (hyperfocal distance) into the photo, this will make everything sharp.
Use a polariser. Turn it until the sky darkens. It will work best at 90 degrees to the sun. There might be banding if used on wide angle lenses.
Use the rule of thirds as a guide. Put the horizon on a third line to create a more interesting photo. And remember rules are made to be broken !
Think about your foreground, middle ground and background. Fill the frame.
Shoot early morning or late afternoon. The light is softer and you don't get harsh shadows.
The best time for landscape photos is 20 minutes before and after, sunrise and sunset.

Action

Use a high ISO to keep your shutter speed up and freeze the action. Minimum shutter speed for freezing would be 1/1000sec. and for some blurring of legs, 1/500.
Use a telephoto lens to get in close and fill the frame.
Use a monopod to support your telephoto lens.
Learn to anticipate the action. Unless your camera is one of the top professional cameras, there will be a delay between pressing the shutter and taking the photo. With practice you will learn when to press the shutter to get the moment you want.

Macro

Night

Using a tripod is very handy at night. Because of the dark, more light needs to be let in for the camera to take a photo. Because of that need for light, the shutter needs to be held open longer as to let light in. When the shutter is open, any movement will cause blurring of your photo. Putting the camera on a tripod lets you keep the camera still and give you sharp photos no matter how long the shutter is open.
When shooting cities, photograph about 20 minutes after sunset for night shots. This is when the light in the sky balances the city lights.
Try shooting on a cloudless night with full moon.
Use mirror lock up, if your camera has it, to reduce vibrations from blurring your shots.
Use a tripod. A good quality tripod will feel solid when you lean on it.

Astrophotography

Astrophotography is a specialised type of photography that entails taking photographs of items in the night sky such as planets, stars, and deep sky objects. Astrophotography is used to reveal objects which are too faint to observe with the naked eye, as both film and digital cameras can accumulate and sum photons over long periods of time. - from Wikipedia

Online guides:

Canon BeBit EOS DIGITAL Astrophotography Guide