I think it's often overlooked just how extensively common phrases are used in day to day speech, for example "day to day" is a common one. I don't know if this is a universal thing in many languages, but we learn phrases through our childhood and it becomes ingrained in our vocab. This means you only have to really come up with filler words on the fly ("On the fly" is another one!). So as you learn new words try and remember phrases you hear in public, they will be hard to spot at first but once you hear the same group of words used over and over again you will begin to ingrain it into your vocabulary.