Easy - When you start to feel bored of building and feel like doing something else, get a timer, set it to around 30-50 minutes, maybe 20, then do something else and entertain yourself. When the timer rings, start to give yourself a mental flashback of your progress - don't open Blockland just yet. Visualize what you remember building. Now, visualize the completed project of what you want to build.
Open Blockland and compare the differences between what you remember building, what the finished version will look like, and what it looks like once you've taken a break from it.
I mainly use this strategy with writing stories, but it's worked for building too.