This what we did when we had the first parakeet (as adisvedadvised by the seller):
Keep it inside the bird cage for at least one week, so he starts to feel it as "home". Interact with home as wished, but do not release him. He will also learn that the cage is the place where the food is.
When you release the bird in the room, confine it to only one room - preferably one of the smaller rooms you have.
Do not feed the bird while outside. Hunger will ultimately bring it back inside the cage.
Never mock the bird for being stupid for getting inside - it will understand, feel bad, and ultimately refuse to get back inside again. Instead, praise it when he returns.
Make it a rule that in the evening it has to go inside to sleep. It increases the "at home" feeling.
(optional) You might want to feed the bird frofrom your hand, while it is in the cage. It will learn to trust you.
Never do anything to scare the bird. No sudden moves, no bursts of loud laughter, etc. while in the accommodation period. It will associate the cage with fear.
Find (small) things that really attract the bird (be sure that the bird cannot swallow them or pieces of them. When the time comes, tease the bird with those things to attract it, and then place the thing inside the cage.
Place a mirror inside the cage, and cover / remove the mirrors in the room.
Place some of the preferred food inside the cage - obviously, the preferred food should not be given to the bird just before going in.
