At about the age of two, just about every child desires to have more control over their life. They want what they want when they want it and are going to get very frustrated when they are told no. Some children handle this frustration quietly. They may sit on the floor with a dirty look and refuse to move or become tight lipped when asked to eat their dinner. Other children become violent and will hit, kick or even bite, and some will become very vocal. My son falls in the latter category. When he doesn't get his way, he is that child who screams at the top of his lungs sending chills down your spine. Many years ago, I worked in the toddler room of a day care and have experienced all of these types of behaviors. I have learned a few tricks to help ease this transition for both you and your child.
The best thing you can do for your child is give them a choice. Your child just wants control so make them think they have it. Is it time to clean up and your child is telling you no? Then don't tell them to clean up. Ask them this instead, "Do you want to pick up the cars or the books?" They get a choice and you get the room clean. Is it time to get ready for bed but your child doesn't want to sleep? Ask them, "Do you want Mommy or Daddy to help you tonight?" or "Do you want to wear your red pajamas or the blue pajamas?" Of course you will alter these questions to fit your particular situation but the point is, don't tell your child what to do. Ask them a question that gets them to make a choice you will both be happy with.
Of course you can't always give your child the ability to choose. Sometimes you will need them to just do what they are told. This leads me to my second tip. Give your child a 5 minute warning. I could not get through the day without this trick. A perfect example is when you have to leave a public place without your child trowing a fit. 5-10 minutes before we need to leave I simply say, "Johnny, we are going to leave soon so finish what you are doing." This simple statement lets him know what is about to happen so he is not surprised or interrupted when we want to leave.
Finally, be consistent. I think this is the most important thing you can do. It won't always be easy but you have to stick with it. By remaining consistent, your child will get through those terrible twos faster than the child who gets his way all of the time.