Cockatiels: deserve as much respect as their bigger cousins, Just like the big parrots, each little being has it's own personality and fears. It should be allowed to exersize and that is done best by flying. Flying birds have less fear because they know they can take flight if a preditor comes along. You are a giant so you are the preditor.
A new bird that can fly can be turned loose in a parrot proof room before going into it's cage. It will fly until it is tired. When it lands on the floor it will either step up or allow you to scoop it. Just like the big parrots do not reach for them from above. Use a two hand scoop to lift him with your thumbs on the wings so they won't flap and hurt themselves.
Cockatiels bite more often then the large birds. That is the only way they can tell you no. Each bite will determine how scared it is. They can bite for you to feel it or they can bite to bring blood. If it brings blood it is your fault and you need to think about what made it that scared.
When they start loosing their fear they may do a chomp. All my parrots do it. It is like they are going to take a big bite but just hold on and "taste" you with their tongues. This is to better know you.
Parrots are all afraid of hands but they like to talk to faces. You should give him a perching place at face level to lessen their fear. Even the very scared ones will like to talk to your face as long as your hands are not near.
Parrots are social. They are born into, raised by and taught by the flock. You are now flock leader. The more time you spend with it the better. Even if you are very busy if you are in the room you can be watched and learned. Diet is discussed in other places in the forum, If your bird comes to you on a no veggie diet you will have to teach it to eat veggies and fruit. That is done by eating with it. I believe that parrot humans get healthier when they eat with their birds because they eat more fruit and veggies while teaching their birds
Just like a little kid, you have to learn it's personality to know how to deal with it.
Respect it's space. It is the only thing the bird has of it's own.
Learn it's personality so you know what it needs.
Be visible as much as possible so it can learn your personality.
Teach it as you would a scared child. It will learn things even when you are not paying attention.
Be careful how you talk. If you use bad words it will learn them and repeat.
Like a child use the same words. Do you want out. It is out time.
Feed it the same time every day and a little more than you think it can eat.
This is how I treat a healthy bird. My flock include refugees and crippled birds. Some came from very dark places. The really scared ones disappear into the flock and learn from them before it will come to me but it will come to me in it's own time.
That is all I can think of right now. I hope my bad spelling does not confuse you. I am just helping with learning the bird. Pajarita and the others will give you info on diet and lighting.