The most important item needed before your feathered friend is brought home is a bird cage. Remember, even birds that come out of the cage to socialize spend a large part of the day in their cage. Bigger is better as long as the spacing between the bars is narrow enough to prevent injury if the bird tries to escape. The bird's head should not be able to fit between the bars.
The door needs to be large enough to comfortably put your hand through, catch the bird, remove the bird, and replace the bird. The latch on the door needs to be escape-proof as the bird is going to have a lot of time to find a way to open it. Some owners place a clip or a padlock on the door of their escape artist's cage.
Budgies like to move around and should have a cage that is tall and wide. Canaries and finches like to fly and should have a cage that is wide and long to allow for flight. Cockatiels need a cage that is big enough so the crest on the head and the long tail fit without being crushed. The size recommended at most pet stores is going to be the minimum size for that species of bird. Your bird will be happier with a larger, more spacious cage.
Cages come in various styles (corner cage, octagon, square, rectangular, etc.). Remember to keep your bird's size needs in mind when making your selection. Metal is usually the best material as it stands up to the abuse birds give it and is easy to clean and disinfect. Avoid lead-based paints or cages made with zinc, as these can be toxic.
A sliding bottom tray is commonly seen in bird cages. This should be easy to remove, clean, and replace with no gaps that the bird can escape through, either while the tray is removed for cleaning or while the tray is in place. Newspapers or Cage Liners are commonly used to line the tray and should be changed daily. Some owners will use small animal bedding. Don't use wood shavings or chips as they are dustier and can irritate your bird's airways. Bedding made of shredded paper or cardboard works well. Towels can be used in a pinch as they are easy to clean by tossing into the washing machine.
Keep the bird in a sunny, draft-free area. If the bird is more social, keep it in an area of human activity. If the bird is less social, it may be happier in a quieter area of the house.
Place the cage so the bird perches at about your chest level. Lower than that (especially if placed on the ground) and the bird will be anxious and feel vulnerable. Don't place it higher than your chest level as 'higher' means 'superior' to birds. In the wild, the more dominant birds perch on higher branches.