Deliver real, end-to-end working functionality, at least every two weeks and ideally more frequently. Unless and until the code is used it's all meaningless. This more than anything will protect you from overengineering or building the wrong thing, which are the biggest dangers.

Delay design decisions as late as possible. Unless and until you need to make a decision to allow you to deliver some real functionality, don't make it. Avoid any planning of things like code structure. This will give you the chance to make better decisions, since you'll have more knowledge at the point when you make them.

Reduce the number of lines of code. People will say that other things are more important, that making the code longer can sometimes make it more readable. That's an intuitive view, but in my experience it's wrong. Reduce the number of lines of code, and everything else - good design, good code structure, good language choice - will follow.