DO'S
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1.  First line of a main script should always be:  <?php
    IE, do not start in HTML mode.
    Turn on error reporting, tied to an if ($debug).
    Turn on logging.

2.  Command line php for cases where the browser produces no output.
    However, will not execute with references to $_SERVER, $_GET,
    $_POST. 

3.  All top level scripts should FIRST check if a user is logged in; if
    not, use a 'header("Location: ...")' directive to switch to a login
    script.

4.  Clearly distinguish between top level scripts and libraries.
    Each subdirectory should have an index.php file (usually using
    redirection)  to prevent browsing the directory.

5.  Always guard against sql-injection and cross-site-scripting attacks.

6.  Use your state diagram for forms processing. 

7.  Store machine/userid/password/database name in a separate include
    file.  Enables easier switching between development, test and
    production machines.


DON'TS
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1.  Here strings -- Ex. 1.3, p. 2.
    Error prone.  Messes up program indentation.
    Or, at least put them in an include file by themsleves.

2.  Do not switch into and out of HTML mode in a PHP file (and vice
    versa).  Use an include instead.