Roughly, by doing sufficient quality scientific work so as to not only demonstrate sufficient knowledge of the field of study, but also a demonstrated ability to objectively analyze the work of others pursuant to the rules of scientific inquiry.
Most papers are sent to two or three referees, but some are sent to more or, occasionally, just to one. Referees are chosen for the following reasons:I think that every publication has its own rules, but the concept of peer review is pretty much the same everywhere.* independence from the authors and their institutions
* ability to evaluate the technical aspects of the paper fully and fairly
* currently or recently assessing related submissions
* availability to assess the manuscript within the requested time.
demonstrate to whom?