MathMan 13: Your problem is very common! I find having a designated quiet corner to be helpful. When a student acts up, have the student sit in the corner until he or she calms down. More often than not, misbehaving students will be on their best behavior for the rest of the day. 

TeacherPro 90: I recommend having a special quiet signal. When I want my students to be quiet, I raise one hand in the air and cover my mouth with my other hand. One by one, students will copy my quiet signal. In a short period of time, all students will stop talking.

 SchoolLady 3: Be consistent when enforcing class rules, and follow a routine. For example, my students are supposed to be quiet when getting in line. If they talk, I have them sit back down. I explain to them that they need to start over and line up again. The second time, students do so quietly. Repetition is the key! If students follow the rules particularly well, I reward them. For example, we might take a break to play a fun game together.