Privacy involves how safe your private data are from "spying eyes" -- that is, if they are really "private" to you and those whom you willingly trust with them. While a "normal user" is unable to tell how safe an app is in this context, there are several apects he/she can take care of -- or where one can check, e.g.:
- only install apps from trusted sources (minimizing the risk of trojans and other malware)
- checking user reviews before installing an app (see if it showed "conspicious behaviour" in the past)
- checking the permissions an app requests. When in doubt, and no explanations are found on either the app's page at google-play-store or the developers website, don't hesitate to contact the developer. No answer is an answer as well. If the dev says "Don't worry, that's just needed for ads" -- that's not necessarily a relief (see Risks involved with permissions)
- Don't hesitate to buy an app, if there's a pay-version without an "ad module" attached. This increases your privacy level (again, see the Risks involved article on our site for details)
- if you find anything "conspicious" not covered here or answered otherwise, feel free to raise the topic posting a question. This is the tag for you in these cases.
And then there are the "after-life" issues. No, I don't talk about your health -- but about "you and your device living together". Once you've got a new device, you might have no need for your "old device" anymore. So before giving it away, you might want to read this :)
- Is there a list that explains the risks involved with each granted application permission type?
- Why do so many applications require permission to read the phone state and identity?
- I have sold my phone on eBay. What should I do before I send it off?
- What information does stock Android send to Google by default, and how do I opt-out?
- What's the most complete way to erase all the data from my phone so it cannot be recovered?
- Google Account activation: What should I consider concerning privacy?
It neither hurts to check out our most frequented questions on this topic :)