• Never assume setup

This one is a bit broad. It refers to a wide variety of topics and situations. For one, it refers to responsive web design. You should consider users who are accessing your webpage from a myriad of devices with different size screens. I am writing this post from an older laptop that has a display resolution of 1024×768 (a 4:3 aspect ratio!). Some websites automatically display things in a way that is sensible for users like me, which is good!

However, it isn’t just about people who use old laptops with low screen resolution. Consider phones that sometimes have really large screen resolutions but tend to be used in portrait mode (a very different aspect ratio!) instead of landscape mode. You’d know a mobile unfriendly website immediately if you were using a phone simply because you’d be forced to pinch and zoom out in-order to see the page content. Then you’d probably have to zoom in so that you could press buttons! So please, do some responsive website design!

• Don’t trust user input

This is more of a back-end problem than a front-end problem. All the same, it is vital to sanitize and filter out special characters from user input otherwise you risk cross-site scripting attacks and SQL injection. Not fun!

• Never put sensitive information in the URL

This is admittedly a rookie mistake. It happens occasionally, however, and it’s dangerous. Do not put user passwords into the URL bar.