You've learned to write some basic HTML, CSS, PHP/Python/Perl and SQL, found a hosting service, and are ready to create your first LAMP web application. You've already read a bit about security (you know always to escape user-supplied parameters, etc.). Here are a three very simple tips that will help you along right at the start, without getting caught up in religious wars about frameworks, MVC, REST, abstraction, object orientation, etc.

The tips (summed up) are:

• Keep all the database code together
• Make an extra database for junk.
• Make GET harmless.

...with the requisite explanations for each.