How I can efficiently use Google Scholar to find prior research on a topic?
It is true; there are too many papers out there to even read the abstracts of all of them. That is why many research papers contain phrases like "to the best of our knowledge", etc. 

My approach to minimize the risk of missing out publications is as follows: I start with reading review papers. These will sum up the research up to a certain point and will show you what the seminal papers in the field are. Then I look up the latest papers that cite the reviews and/or the seminal papers. This approach works very well with Google Scholar.