We are running a mobile app and we want to find out how we can get the most value from the reviews we receive, how to treat them as valuable data in order to take decisions from there
In general, you should listen to your customers and try to understand any UX factors that are triggering their experiences. The simplest way to deal with this is to read the reviews and keep in mind the factors. However, if you want a formal system, you could list factors in a spreadsheet or on a whiteboard, and keep a counter each time someone mentions them.
In my experience any real problem will be brought up regularly enough, and so the simpler version of just reading the reviews and keeping them in mind has worked well, even for an app with over 10 million downloads.
Keep in mind however, that the reviews and ratings are just one of many tools, and you shouldn't rely purely on them for your UX feedback.
That said, feedback from ratings and reviews have characteristics that you need to keep in mind:
People with a problem are more vocal than people without the problem. So if you've made some UX decision and 90% of users love it while 10% hate it, you will likely hear more feedback from people hating it. You shouldn't use this as an excuse to ignore negative feedback though.
Different cultures have different tendencies in ratings and feedback. For example, Germans tend to give lower ratings than Americans. We often get ratings that say something like "Great app, I love it!" and get 3 stars from German users. Whereas my may have a rating like "Okay, could have been better" and get 4 stars from an American user. In Brazil on the other hand there seems to be a trend to give reviews like "Great app, best thing ever!" and give 1 star - we get about 10 of these a day, and they are almost exclusively from Brazil.
Feedback will generally be on simpler issues. So if someone doesn't like round avatars, you'll hear about it. But if someone finds the navigation structure suboptimal, you won't likely hear anything about it.