1. Use a Coding Standard

Global variables and loops are a mess and can prove problematic when your application grows to millions of lines of code (which most do!). They may influence code elsewhere that is difficult to discern, or cause noisy naming clashes. Think twice before you pollute the global namespace with variab...

It's easy to overlook writing tests for a simple application, but as they grow in size it becomes increasingly important to be sure a change in one location after a time doesn't break something. Having tests makes sure the specific process you're testing always stays functional as intended.

Comments are crucial. You won’t appreciate them until you leave your thousand-line script for a couple of days and return to and try and make sense of it. Anyone who can read code knows WHAT the code is doing. Explain WHY you've done it this way. 

Managing changes and revisions should be easy but effective, so pick whatever version control software that will work best with the workflow of your development team. I prefer using a distributed version control tool like Git or Mercurial; both are free software/open source and very powerful.

Try to use tools like Ant or Phing to get your source prepared, compressed, and deployed. Building your whole application with a single command is a marvelous way to prevent errors and omissions that are inherent when performing repetitive tasks.

Never use names like $k , $m , and $test for your variables. How do expect to read such code in the future? Good code should be meaningful in terms of variable names, function/method names, and class names. Some good examples of meaningful names are: $...