You can't make an application backwards compatible if you don't have a previous one, but here are some tips:

  • Stick to the general programming language rules/standards,
  • Use easy and understandable names for classes, functions, etc,
  • Document your code,
  • Separate your database functions from your website functions, and separate the HTML from your code as much as possible (work object oriĆ«nted).

That's it.