If you can, you should prepare the cage in anticipation for the arrival of your new budgerigar or budgerigars if you have decided to get more than one. The cage need to be washed first before it is used, wash the cage in hot water using a disinfectant that is designed for bird cages, normal household disinfectants, detergents and soaps could be harmful to your bird. All second hand cages MUST be disinfected before use and dry the cage thoroughly before use.
The basics of how to set up a budgie cage is as follows. The floor of the cage needs to be laid with newspaper and then sand paper and covered with sprinklings of gravel. Then put in the perches, water, dishes for seeds and grit, millet, mineral block and cuttlefish need to be clipped to the cage bars.
The perches should be arranged so that they are in easy reach of the food and water bowls, the budgie needs to be able to drink and eat without performing an acrobatic feat. Keep the perches far enough away from the bars of the cage as to ensure the budgies tail does not constantly rub on the bars.
You will usually come way from the pet shop with your budgie in a small cardboard box with air holes. To get them out of the box and into the cage in the simplest way is to place the box inside the cage, open one of the flaps and wait. If they do not come out of the box within say an hour then you should carefully tilt the box to edge them out making sure not to scare them. Leave the bird to get used to its new environment in its own time, do not keep approaching the cage every 5 minutes saying "who's a pretty boy then?" they will want to see what happens in the room that is now they're home and will enjoy observing you from a distance at first. After a couple of days you can start approaching the cage and talking in a calm voice to your budgie, this will reassure them that you are friendly.