1. House both birds in their own cages in the same room. This allows them to get to know each other from a safe distance.
2. Create a pleasurable association. For the first few days have separate play and training sessions for each bird. Then, twice a day , move their cages closer together. If either bird looks stressed, move the cages apart until they both appear comfortable. Alternately hand out small treats that the birds can eat quickly. After a couple of minutes, move the cages apart and stop handing out treats. They will learn that good things happen when they are together.
3. Treat your existing bird as special. This will help him remain confident in his place in your flock and help combat unwanted behaviors. Greet him first, feed him first, and attend to him first. But be sure to give each bird equal amounts of your time, while reassuring your existing bird that he has not lost his place in the flock or in your heart. In two weeks begin rotating the position of special bird for the day. No one enjoys being last all the time and the new birds should feel important too.
4. Eventually allow the birds to exercise outside their cage at the same time. A new playstand is great for this purpose, as it provides a "neutral" space for them to socialize and play together.
5. Watch body language closely for signs of negative emotional valence. Closely monitor both birds and be alert for pulling feathers, biting, screaming, and lunging. If these behaviors occur, separate the birds immediately. Look for signs of stress that may be less obvious, like excessive self-preening or toenail chewing.
Adding a new bird to your flock is a wonderful way to reduce loneliness and promote natural social behavior. But is not without its challenges.
This is an article from Kashmir Csaky who is an IAABC Certified Parrot Behavioral Consultant and a Parrot Division Chairman in Lynchburg, Virginia.
(This is only a recommendation from one source. Please pay close attention to your birds behaviors. Some birds just will not get along. Thank you Chirping Friends)