There are three sure-fire ways of getting your courses appearing near the top when users do a search.
- Have a top-rated, or near top-rated course.
- Have a best selling course.
- Have one of the only courses available in some particular area of interest
I cannot tell you exactly how Udemy decides to put courses near the top of the results page when a search is done, but the three factors I've listed play very important factors. And, accomplishing the first two can take a great deal of time.