The file should be named according to the language it was written. The name shouldn't be abbreviated too far (`Javascript.js` instead of `JS.js`) and it shouldn't be abbreviated to little (`CSS.css` instead of `Cascading Style Sheets.css`). Additionally, hyphens should be used instead of spaces (`Objective-C.m` instead of `Objective C.m`).
The code in the file should be the simplest or most straightforward way to print/display/show `Hello World` exactly once in the language used. Input from the user shouldn't be asked for where possible and a newline should only be printed when necessary.