Even if you're not using a statically typed language, if you're working on a project, take some time to really think about your input data, intermediate data (subsets/transforms that you'll need for your internal functions), and output data first, before you really start coding. Don't just start coding without an idea of them. They don't have to be final of course, but at least clarify it before you start.

I always struggled with this in the past and considered data the hardest part about programming. How is your input data structured, how do you change it throughout the code, where do you need what aspects of the input data, and so on. That's really what complicates code. Simple and clear data results in easy code, and types facilitate that.