PHP Coding Standards (pear.php.net)

Always use to delimit PHP code, not the <? ?> shorthand.

<?php ?>

Control statements should have one space between the control keyword and opening parenthesis, to distinguish them from function calls.

if (true) {
   switch (condition) {
      case 1:
         action1;
         break;
      case 2:
         action2;
         break;
   }
}

You are strongly encouraged to always use curly braces even in situations where they are technically optional.

if (true) {
   // single line stuff
}

Split long if statements onto several lines keeping the question mark and the colon at the front.

if (($condition1 || $condition2)
    && $condition3 && $condition4
   ) {
   //code here
}

There should be one space on either side of an equals sign used to assign the return value of a function to a variable

$long_variable = foo($baz);

The CS require lines to have a maximum length of 80 chars. It is allowed to split parameters in function calls onto several lines.

$this->someObject->subObject->callThisFunctionWithALongName(
   $parameterOne, $parameterTwo, $aVeryLongParameterThree
);

The same applies not only for parameter variables, but also for nested function calls and for arrays.

someFunction(
   array(
      "foo" => "bar"
   )
);

To support readability, the equal signs may be aligned in block-related assignments:

$short     = foo($bar);
$thelonger = foo($baz);

Class and function declarations have their opening brace on a new line:

class Foo_Bar
{
}
function doThing()
{
}

Arguments with default values go at the end of the argument list.

function doAnotherThing($id = 0, $doAgain = false)
{
}

include_once and require_once are statements, not functions. Parentheses should not surround the subject filename.

include_once "/file.php";