@Rumani, you can set test case priority in TestNG by using priority attribute to the @Test annotations. In case priority is not set then the test scripts execute in alphabetical order. Following code snippet prioritize the test cases:
package TestNG;
import org.testng.annotations.*;
public class PriorityTestCase{
    @Test(priority=0)
    public void testCase1() {  
        system.out.println("Test Case 1");
    }
    @Test(priority=1)
    public void testCase2() {     
        system.out.println("Test Case 2");
    }
}