Quality of your ad: Relevant landing page experience and CTR are the essential things for the ranking of your ads.
Search Context: your device, different terms and time of the day also have a strong impact in raking.
Ad extension: ad extensions are the important factor in a ranking like how relevant they are and how they produce the CTR.
Google AdWords basically a place of auction where you can bid for your desire ads and in the end the winner is the bidder with the highest bid.
As you know the ins and outs of ads of the ranks here are the 3 important ways so you can improve it without spending more on clicks.