There is ALOT of information out there in books and on the internet on interacting ("taming") parrots. I have found that most of the handling techniques for larger parrots aren't really needed or understood by cockatiels. This is where you can make or break a cockatiels confidence in you.

EACH COCKATIEL IS AN INDIVIDUAL. There is no "one way" or to work with them. You need to learn to think like the cockatiel and then you can make progress. This means you must slow down and observe your tiel. Allow for it's preferences and personality to come out.

1. Use the "up" command (or whatever works for you) whenever picking up the tiel. I have found that with my tiels, some will respond to one "up" and others respond better to a succession of "upupupup", especially younger tiels who are just learning.
2. Never place the cage or playgym up so high that you have to climb to get to it.
3. Don't pass your tiel around like a new toy when people visit, especially people that they have never seen (would you do this with a 1 year old child???).
4. Keep your cockatiels wings clipped if you do not have a separate safe flight area in your home. It is very sad to hear about how many birds are lost by flying away through an open window or door. A cockatiel will not survive the elements or predators for long. An unclipped tiel can be injured or killed by crashing into a window or wall. Even if purely accidental, these situations are tragic. Some tiels need less of a clip than others. If you leave your cockatiel fully or partially flighted, you are responsible for making sure that he or she is safe from escaping the house, flying into ceiling fans, toilets, hot water on the stove or in the sink or getting stepped on/shut in doors, etc. Please visit the Bird Hotline to see lost birds or report a lost bird.
5. If you are too specific with “out time” or let a very dominant tiel come and go from it’s cage on it’s own, you could be creating trouble. If you stick to exacts, the bird will expect exacts (after all, that is only fair for them to assume!), and will be upset if you vary the schedule. It will also be upset if you decide to put it back into the cage when it is used to being left out all day and will most likely voice it's opinion by trying to get away from you or with a hearty nip. Again, I stress that you gauge your tiels personality. Keep in mind that cockatiels get in different moods and go through different stages during their lifetimes. How they were one year may not be exactly how they are the next. Be willing to accept these changes in their behavior and adjust to them accordingly. In general, though, most cockatiels are fun-loving, happy little parrots.
6. Do visit and greet the tiel immediately upon reentering the house or room. Cockatiels are flock creatures, and they miss their companions! I call to them when I come in the door, no matter how long I have been gone. This does not necessarily mean taking them out or making a big to-do over it. Just speaking to them is sometimes enough to keep them happy in knowing where you are. When they give the contact call, call back to them. All of my young tiels get taken out and reassured when I come back home after being out for a while. As they have gotten older, they are mostly content with me talking to them. Sometimes they are wanting a quick cuddle. I watch their body language and act accordingly.
7. Cockatiels love to squalk, talk, and whistle (or even scream) to their humans, especially if you leave the room. Try creating a "special" call between you and your bird to make it easier for you, as the human, to tolerate. A wolf whistle, word like "pretty, pretty", or for the more non-wordy females, just saying their name back as they call will suffice. I try to let my birds know that, yes, I am still here and all is well in the flock. We even have a “loud” time in the morning when we all are happy and noisy sometimes.
8. REMEMBER--WE HUMANS HAVE PLACED ANY CAPTIVE BIRD IN UNNATURAL LIVING CONDITIONS. It is up to us to make them more comfortable in such an unnatural habitat. They cannot think like us, but we can learn to think like them. Cockatiels are, in general, wild creatures. They fly many miles a day in search of food and water in the wild. It is up to us to provide the best that we can to keep them happy and healthy.
9. NEVER NEVER NEVER hit your cockatiel. This will ruin the trusting relationship. Birds don’t comprehend “hit” and will most likely retaliate with aggression and most definitely fear!
10. NEVER scold your tiel for regurgitating for you or trying to "mate" with you. These are natural behaviors showing affection to their mate. DISTRACT them and place them on another area of you or a playpen. They will not understand being punished for it. I neither encourage nor discourage it. I just move on to something else. For instance, if your tiel tries to "mate" with your hand, then talk kindly and place them on your lap or on a playstand.
11. NEVER scream at your bird in anger. Cockatiels get very afraid at harsh, loud words. While I have been told that the larger species can actually enjoy this “human tantrum”, I have noticed that cockatiels differ from this and get extremely upset whenever there is conflict around them. If you are having a bad day, say hello and tell the bird how much you love it. Then you can go and sulk. Actually, my birds help to keep my spirits up!
12. DON'T PUNISH your tiel and expect it to connect the punishment with the thing you call "wrong". They don't make connections like that (as a very young child does not). DISTRACT, DISTRACT, DISTRACT. It is up to you to keep them from doing things first.
13. Do not use laddering (repetitive ups on alternating fingers) as punishment. Continuous laddering only frustrates them and loses their attention--they don't learn once you have gotten this far.
14. Do not cover the cage in punishment. Covering the cage may quiet the cockatiel, but they won't necessarily make the connection as to why they have been covered. Most cockatiels scream out for a reason. You must try to find out that reason before acting out. Sometimes they are just overly stimulated. Some of my tiels have gone through stages where they scream more than usual and then they are through it.
15. Don’t be a scrooge. SHARE, SHARE, SHARE with your tiel. They are flock creatures who enjoy doing things with the flock like eating, bathing (not in a tub or in the direct spray of the shower), and just plain "hanging out". This helps immensely with the bonding process.
16. Car rides are nice to go on together. It is not cute to have a tiel in the car out of a carrier, though. Place them in a carrier and seatbelt it in securely. Yes, I was in an accident once, and if Mr. Merlin had not been in his carrier, I would have most likely lost him. I have found that when outside or in the car my tiels like to be in a carrier that is not totally open. Provide a carrier with a solid back or cover part of it for security.

This is a question that is asked very frequently. One of the most popular is "Which one is a better talker?". Hands down it is the male, but, I have 2 females that talk when they feel like it, too. I thought that this was a genetic thing with Peep and MiniToo since they are sisters one year apart. Then, this year, after I bred Ziggy and Angel and sold 2 of their babies to a close friend of mine, I was happy to find out that their female, Bonnie, the cinnamon pearl from the clutch is starting to form words. Yes, I have been there when she talks. Both of the babies, named Bonnie and Clyde, still remember and love me, and both will talk to me when I come over to visit them! So, my guess is that it is the way that the tiel is raised versus the sex. Males form words better than the females do, I will attest to that, but the females will try their hearts out. You cannot make any tiel talk, they have to want to talk. So, when choosing the sex of the bird, if you want a more clear voice, males take the blue here. When it comes to loving you, both can be loving, it depends on the individual bird, so I don't really choose by sex.
I have found that my males can be more moody than my females. Keep in mind that there are exceptions to this. Noogie loves nothing more than to be scritched. He is my only cockatiel that you can touch anytime, even at the cranky bedtime.