When making a home for your feathered friend, your first consideration should be the size of the cage. This largely depends on two things: the species of bird, and how many birds will be sharing the cage.
The bar spacing is particularly important, as bars that are too wide can let your pet escape or injure itself trying to get out. Bear in mind that accessories like perches and toys will fill up the space quickly, so it's best the get the biggest cage you can accommodate and increase the size accordingly if you plan to have more than one bird sharing a cage. Many modern cages have detachable litter trays, which not only make cleaning easier but also stop your bird from eating food that has fallen into waste.
Stainless steel wire-framed cages are a popular choice as they are easy to clean, non-toxic and durable. While wooden cages may look nicer, they can splinter and painted cages can be harmful to birds if the flakes are eaten. The cage should be placed somewhere away from temperature extremes - away from radiators, direct sunlight and draughts. It's also best to put them well away from any potentially harmful chemicals or anywhere cleaning sprays might be used.
Once you have your cage, the next step is to make it into a home for your bird. Without making the cage cramped, you should give it a good number of perches and toys, which help to keep your pet mentally stimulated. Birds tend to feel safer the higher up they are, so make sure at least one perch is placed high in the cage - this will often be the one they choose for sleeping. Some species need nest boxes and all will need water for drinking and bathing.
If you plan on keeping more than one bird in the same cage, it's best to get one that's designed for the purpose - some have partitions to keep your birds apart if necessary.