Xib界面

MyViewController *vc = [[MyViewController alloc] initWithNibName:@"Xib名字" bundle:[NSBundle mainBundle]];
[self.navigationController pushViewController:vc animated:YES];

Storyboard界面

UIStoryboard *sb = [UIStoryboard storyboardWithName:@"Storyboard名字" bundle:[NSBundle mainBundle]];
MyViewController *vc = [sb instantiateViewControllerWithIdentifier:@"Storyboard ID"];
[self.navigationController pushViewController:vc animated:YES];

补充：

1、UIViewController 的xib调用：

//加载以UIViewController为基类的控制器MainViewController的XIB时：
MainViewController * main = [[MainViewController alloc]initWithNibName:@"MainViewController" bundle:[NSBundle mainBundle]];

2、UIView的xib调用：

//加载以UIView为基类的子视图BaseView的XIB时：
BaseView * base = [[[NSBundle mainBundle]loadNibNamed:@"BaseView" owner:self options:nil] firstObject];