Reusable Scripts
One of the most helpful aspects of creating any FileMaker solution is taking the time to create reusable scripts as you code along. While it does take a bit more effort to think things through, it creates a repository of resources you can pull from any time you start a new project or add a similar feature to your current one.
Leverage is what you're after. If you've seen any code you've written once before, and you start to enter that same code somewhere else, then you need to figure out how you can isolate the code so it can be reused.
In this video, I walk through the steps I take to make sure as much of my code (scripts and calculations - including custom functions) can be reused.