Explaining in advance what's right or wrong about a behavior is no more effective than feedback. Technically speaking, that explanation in advance, when used all by itself, is an antecedent with no consequences. An antecedent is anything you do to set the stage for a behavior, to prompt it to occur; and consequences are what happens after the behavior—reward, praise, punishment—that teaches a child to do it again or not. An antecedent without consequences doesn't do much to change behavior.
Fortunately, science does tell us how to change behavior and how explanation can be used most effectively. (Those who wish to see the scholarship can find the relevant research, much of which has been published in the Journal of Applied Behavior Analysis, cited here, or they can read my far more accessible distillation for lay readers.)
You begin by deciding what you want the child to do, the positive opposite of whatever behavior you want to stop. The best way to get rid of unwanted behavior is to train a desirable one to replace it. So turn "I want him to stop having tantrums" into "I want him to stay calm and not to raise his voice when I say no to him."
Then you tell the child exactly what you would like him to do. Don't confuse improving his behavior with improving his moral understanding; just make clear what behavior you're looking for and when it's appropriate, and don't muddy the waters by getting into why he should do it. "When you get mad at your sister, I want you to use words or come tell me about it or just get away from her. No matter what, I want you to keep your hands to yourself."
Whenever you see the child do what you would like, or even do something that's a step in the right direction, you not only pay attention to that behavior, but you praise it in specific, effusive terms. "You were angry at me, but you just used words. You didn't hit or kick, and that's great!" Add a smile or a touch—a hug, a kiss, a pat on the shoulder. Verbal praise grows more effective when augmented via another sense.
If you don't see enough of the desirable behavior, then you can work on it using simulation play. Wait for a peaceful moment and then propose an exercise. "Let's see whether you can stay calm and just use words when I say no to you. I'm going to say no—remember, this is just pretend—and you stay calm, OK?" You can even switch roles as part of the game. Most kids delight in playing the parent and saying no to the parent playing the child.
Your objective is to arrange for as much reinforced practice as possible, which means you want your child to have many opportunities to practice doing the right thing and then be reinforced in the habit by receiving rewards. Your praise is the most important reward, but you can also add little age-appropriate privileges (staying up for 15 more minutes before bedtime, choosing the menu for dinner), goodies (little five-and-dime gadgets for younger children, downloads or cell-phone minutes for older ones), or treats. And, yes, you reward successful let's-pretend simulation sessions, too. This won't go on forever. A brief but intensive period featuring lots of reinforced practice, often somewhere between a couple of weeks and a month, can make long-lasting or even permanent changes in a child's behavior.
Going ballistic never helps, but explanation aimed at improving a child's understanding can actually play a useful part in this approach. When combined with reinforced practice, explanation has been proven to speed up the acquisition of behavior. So, yes, go ahead and explain why it's important to show respect to parents or to play nicely with others. The understanding your child achieves will resonate with the experience of doing the right thing and being rewarded for it. The deep, nuanced science on this topic all points to reinforced practice as the key, but the greater understanding that comes from explanation is an optional add-on that can help good behavior develop more quickly.