If you bought your parrot from a good breeder, the bird should already be used to humans and may be willing to interact with you immediately. Parrots that have been re-homed or adopted from rescue sanctuaries may have been abused or neglected by previous owners. In such cases patience and time are necessary to gain the parrot's trust.
This should go without saying, but many new parrot owners treat birds as if they were dogs or cats. Dogs and cats are predators, and as such have very different instincts to parrots, which are prey animals.
To parrots, any strange person is a potential predator. Aggressive or violent behavior will confirm this suspicion. Physically disciplining or hitting a bird has no place in parrot training—this just creates a fearful parrot.
A common mistake when training parrots is to make extended eye contact. Predators focused on their prey tend to stare at their intended meal. Staring directly at pet parrots can make them very nervous.
Start slowly. You may want to cuddle and play with your new macaw, but she may not be ready for close contact. Instead, sit some distance away from the parrot cage, where the bird can see you. Talk slowly and softly. While you watch her, close your eyes frequently for a few seconds. This tells the parrot you aren't a predator. When she feels comfortable with you she might close her eyes in response to you. Called the "blink game" by some parrot owners, this is a great trust building exercise.
Over time slowly move closer until you're sitting next to the cage. If the parrot becomes upset, she's not ready for you to be that close.
Once you can sit next to the cage, start offering her treats through the cage bars—nuts, fruit and millet sprays are popular choices. When the bird readily accepts treats through the bars you can open the cage and start offering treats at the cage door. Be aware, however, that nervous birds can get very possessive of their cage. You don't want to set back all your hard work by getting bitten.
Gaining a parrot's trust is an ongoing process. If you're consistent in your expectations, gentle but firm in your interaction with the bird, you'll find parrot training goes much easier.