When you submit a paper to be published, the journal will ask you to suggest at least three reviewers. My question is how to search for appropriate reviewers for your paper?
This is actually a good question, with not so obvious an answer as it might seem for some people. If what I've written is too much, you can just look out for the text in bold font.
My first journal paper was published with senior professors who had been publishing in mainstream journals for decades, and had been going to mainstream conferences for decades, and who themselves had well-established mainstream supervisors when they were early in their careers, so they knew what they were doing. I was an undergraduate student and my more senior co-authors chose the referees for that paper.
The next submission I made to a journal was rather unfortunately done completely on my own, as a solo author. I was now a PhD student at a different university, and it never occurred to me that I could ask my supervisor from the aforementioned earlier project, for advice (I should have). As a PhD student, any supervision I got from professors, was far more "hands-off", and people were not as approachable for advice as that undergrad supervisor was (this doesn't have anything to do with PhD vs undergrad, it's just something that varies from person to person). For this solo-author paper, I could try to see if I have a copy of the submission information, but I'm certain I just put something like "No preference, except it would be inappropriate to send it to Person A for the following reason..." where Person A was someone who I didn't want refereeing the paper. I'm 99% sure that they sent it to Person A.
The next paper I submitted to a journal was again with the first supervisor I mentioned, and this it was only two of us co-authoring the paper, and I was a first-author and far more senior than before, so I was much more involved in the process compared to the first time. He said "let's send it out to all our competitors!". Now I'm only starting to realize, while thinking about your question, how complicated referee selection can actually be. In that particular case, the work was of such high quality, that it was pretty much guaranteed to get accepted, and sending it to the leading competitors in the field meant we got excellent feedback while still getting the paper accepted. When I say "competitors", I mean: the very small number of people in the world who were designing exactly the same type of models as we were, but who had extremely strong preferences for their own types of models versus our type. These "competitors" got into long-lasting heated debates with my senior co-author, at conferences, and stubbornly refused to use our model, or admit that it was better than there's. However, choosing "copmpetitors" like this, is not always a good idea.
Typically, for the average paper, people choose referees who they know fairly well (if you go to enough conferences regularly, you meet the same people each year and become familiar with each other, or you meet people through email interactions when discussing each others papers), but not people they know too well such as co-authors, colleagues, former supervisors/students, family members, etc.
To conclude: people typically learn the referee selection process by the experience of working with co-authors who know what they're doing. If you don't have a co-author like this, then you may want to ask a more senior person near you (geographically or figuratively), who is familiar with the subject of the paper.