What can I do to reach marketing goals, without spending more?

Focus on improving your organic growth. Every install begins with the user arriving to the orginal app product page. When that page is optimized to the max, marketers are able to see overall improvement in their paid campaigns because of the increased user conversions that are occuring.

Where should I focus my efforts on for ASO?

Selecting three high-volume keywords within your app category is a great first step. Utilizing data gathered with paid campaigns allows you to find which keywords users are using to find your app and your competitiors's apps. Once you have decided on which keywords to focus on, creating your ASO around those keywords becomes much easier and can imrpove app relevancy in the app store.