Only about 300 listings show up for any search on Airbnb although there may be several hundred available. For instance, there are about 1300 listings in my city, but you will never get that many to appear in a search. Airbnb shows suggested listings based on a secret algorithm, however, a fairly common aspect is similar listings. If a prospective guest has clicked listings similar to yours, then on their next search you have a greater chance to show. Just about every searcher sees search results a little differently.
Now to answer your question about how to get higher ranking:
1. Update your listing often.
2. Have a good headline that will attract attention, thus more clicks.
3. Write a good, truthful listing that will get you bookings; a good views to booking ratio helps.
4. Make sure your price is competitive.
6. Turn on Instant Book but be prepared to take what you get. (Airbnb will allow you to cancel an IB booking without consequences if you call Airbnb and explain that you are uncomfortable with a guest and let Airbnb hit the cancel button, but you don't want to cancel if at all possible.)
Good luck in your business.