Children who are misbehaving or having trouble with other students need one-on-one time with their teacher to nurture good behaviors and solve their issues. Reprimanding a student in front of their peers can correct some minor problems, but usually there are deeper issues at work in students' lives that need addressing. Make sure students know you are approachable and make time to visit with each student periodically to check in, even if they are normally well behaved. This helps maintain a positive and open environment for your students to develop as learners and grow.
If your class is particularly wild and noisy one day, you may try addressing them in a soft, calm voice. While a teacher's first instinct may be to try to shout over the children and assert dominance, this tactic works because students will always view you as an adult authority figure and will want to hear what you have to say, even if only to disagree with it. While this may not prevent future misbehavior, it is a good way to reign students in order to solve problems in a civilized way.
While your goal as a teacher should never be to lower a student's self-esteem or belittle him, calling on him to answer questions when his attention may be wandering or asking students with extra energy to help at the front of the class can be a good way for children to receive attention they crave in a constructive outlet. Keep in mind that if you call on a student and she is flustered you should try to help her find the right answer and use it as a teachable moment.
If all else fails and you need to assert dominance over your classroom, turning the lights of or briefly flashing them is a good way to get your students' attention in order to address them and regain control.
Students are more likely to behave well when they are provided with a clear definition of what good behavior is. Make a poster that has basic rules of conduct and post it in your classroom in a visible location. Review these rules periodically to remind students of your expectations as their teacher.
Providing rewards for students can be a way to positively reinforce good behavior and set an example for all students in the classroom. While you do not want to bribe students to behave, using occasional incentives like candy or extra free time can motivate your students.