Switch statements:
// Always assume that the case got not catched

// Wrong 

switch ($mode)
{
	case 'mode1':
		// I am doing something here
		break;
	case 'mode2':
		// I am doing something completely different here
		break;
}

// Good 

switch ($mode)
{
	case 'mode1':
		// I am doing something here
	break;

	case 'mode2':
		// I am doing something completely different here
	break;

	default:
		// Always assume that the case got not catched
	break;
}

Operations in loop definition:

// On every iteration the sizeof function is called

for ($i = 0; $i < sizeof($post_data); $i++)
{
	do_something();
}

// You are able to assign the (not changing) result within the loop itself

for ($i = 0, $size = sizeof($post_data); $i < $size; $i++)
{
	do_something();
}