If you want to get far in the game, you'll have to make the most of a precious resource: Celenium. Early on, the easiest way to acquire this is by earning achievements, which reward you with small piles of Celenium. Over time, that can stack up and allow you to invest in builders that will allow your base to function much more efficiently (you should mostly ignore other potential uses for your Celenium). You can sometimes also find Celenium by destroying rocks and trees, so always be on the lookout.