PHP is a famous open source language, which decrease application performance considerbly.

Turn On Error Reporting Immediately during development stage by

Code:
error_reporting(E_ALL);


Single Quotes and Double Quotes are Very Different

echo "Today is the $day of $month";

Instead use the following code :

Code:
echo 'Today is the ' . $date[‘day’] . ' of ' . $date['month'];


Use /*…*/ commenting system to document your code.

It will help in the development of the code or during debugging.