Operators should always be surrounded by spaces with the exception of ++ and --.
$a = 1;
$b += $a;
$c = $a . $b;
$d = $b . 'something' . $c;
$e = $d * $b;
$f = $e / $a;
$g = ($f + $e) * $b;
$h++;
$i--;
Function calls and definitions should not have a space before the opening parentheses.
$x = htmlspecialchars($y);
$item = $DB_site->fetch_array($items);
Function arguments should have a space after each comma.
$x = fetch_something($a, $b, $c);
$i = construct_something(strtoupper('something') . ' ' . substr($var, 0, $b));
Unnecessary spaces around parentheses should not be used.
$var = addslashes( $var );
$str = fetch_something( strlen( $var ), strpos( $x , $y ) );
$x = construct_x(substr($string, 0, strlen($bla)) . '/' . ucfirst($string));
if ($x == 1 AND ($y == 2 OR $z == 3) AND ($a = fetch_x($x, $y) OR $a == 'bla'))