Google is known to accept apps directly without having them go through a review process. However, this does not mean there are no policies you should make sure you're following. Ignoring those policies is actually the best way to get a few warnings (along with your apps being taken down) and your entire account suspended eventually if you don't resolve the issues.

If you're interested in publishing your app to Google Play, you'll want to review the policies first. If you've already published an app without checking the rules in the past, now is your chance. The entire process shouldn't take you more than 30 minutes (even if you're not a lawyer!), so don't be afraid.

Here's the entire list of resources you'll want to check:

This article will not go through all of these policies, and assumes that you're familiar with them to a certain degree. Instead, it will try to discuss some points that are mentioned in the policy, but that you might not think about (either because the policies are a bit vague, or because you've seen other popular apps do it so it sounds fine to you).

 Intellectual property

Using trademarked names/impersonation Making an application for RandomThing? The Google Play policies mention you shouldn't impersonate other products or companies, but it's unclear to many developers that the way you use a company's name in your title can be considered impersonation. For example, you might call your app "RandomThing Browser" -- you're not impersonating RandomThing after all, are you? Unfortunately, it's not that simple. Luckily, it's not too complicated, either: with trademarked names, it's usually best to use them at the end of your app's title and prefix them with "for". This makes it clear from the title alone that your program is not official. So instead of naming your new app "RandomThing Browser", call it "Browser for RandomThing" instead. In similar situations, you should also do the same in your app's description -- don't make it sound like your app is official or endorsed by RandomThing. You should also include the necessary attribution in your description, for example:

RandomThing is a trademark of RandomCompany Inc.

Companies sometimes offer guidelines on how to use their brand name, so make sure to check their website as well. If in doubt, it's a good idea to contact them and ask for more info. For example, Google offers a set of guidelines for using Android related brands (for both the name and icons/logos). Note that some modifications to trademarked names are also not okay (the guidelines offer "G00gle" and "Google++" as examples, and actual apps have received warnings in the past for using part of a trademarked name), since this is considered confusing.
Icons Similarly to the above, you shouldn't use the icon of another product or company (even if you modify it) unless it's explicitly allowed. For example, you're allowed to use and modify the Android robot under certain terms (it's licensed under the Creative Commons Attribution 3.0 license). If you're not sure, create your own icon or use open content (e.g. work licensed under some of the Creative Commons licenses). FlatIcon is also a good resource, and makes it easy to search through, use and provide credit for CC icons.
Screenshots and assets After working hard for weeks, you've finally finished your music player app and want to share it with the world. In order to show how pretty it looks with its gorgeous material design theme and album thumbnails, you decide to take a few screenshots of your favorite playlist… but hold on! Album covers are usually copyrighted, and you shouldn't be doing that. Instead, create original images or use open content when taking screenshots you're planning to use on the Google Play store. The same applies to assets you use inside your app (to give a few examples: resources extracted from a game you didn't make, sounds taken from a movie, etc).

Keyword spam

Your newly made calculator is absolutely mind boggling -- it can do everything! Naturally, you want to let your users know about the endless possibilities, so you decide to list them quickly:

Features: Multiplication, addition, subtraction, division, real/imaginary numbers, powers, graphs, equation solving, functions and more!

… or even:

Keywords: multiplication, addition, subtraction, division, real, imaginary, N, R, powers, graphs, equation solving, variables, functions.

This is considered spam. Instead, write a few sentences explaining what your app does without stuffing keywords:

This calculator app supports all of the normal operations you'd expect from a calculator. It also supports functions and graphs, can solve equations easily and more!

Unrelated keywords are also considered spam. This might sound obvious, but mentions like "Better than ThatOtherCalculator" or "Similar to WolframAlpha" are also considered unrelated keywords, so avoid comparing your app to other services.

Accepting payment/donations through external methods

As a general rule, you're only allowed to use Google Wallet (via In-App Purchases or separate paid keys/"donation" apps). Other payment methods are only allowed for products that can be used outside of the app (e.g. buying books, but not emoji that can only be used by your app). If you want to provide alternate methods to buy your app or donate, do so on your website instead (possibly offering a separate version that checks for the license, independently from Google Play).

The policies still apply to alpha versions of your app

If it's available and distributed through the Google Play store, your application must respect the policies. Don't postpone checking the complete guidelines just because your app is still in the alpha/beta stage -- it being only available to a group of testers doesn't make it an exception.

Advertisements

Many practices are employed by apps all over the Google Play store when it comes to ads. That being said, just because other apps don't follow all policies doesn't make it right for you not to. This applies to all of the above points, but perhaps even more so to this section. You might be used to applications that serve you ads through the notifications system, or add home shortcuts or bookmarks for advertising purposes. You probably hate those apps, but it's being done. Well, if you're considering something similar: don't. Ads must also be clearly separated from your content (so for ads visible at the bottom of your app, put a margin and clearly mark them as such). The user must not confuse them for actual content or risk clicking them by mistake (if they're too close to the real content). Another thing that's worth noting: displaying ads outside of your app is prohibited (e.g. ads displayed after you exit an application).

Final Words

We've gone over a few cases that might not be obvious to many developers, even after checking the policies. This article was inspired by seeing many devs have their apps pulled out of the Play store or their accounts suspended for one or more of the above reasons. It will hopefully be helpful to new and existing developers alike. Again, please note that it's in no way a substitute to the complete terms and policies, even if most of those are common sense. You're highly recommended to check those out in full (links to the relevant resources are provided at the top of this article). If your app has been removed or your developer account has been suspended for whatever reasons, make sure to visit this support article. Last but not least: don't be put off by the amount of policies. A lot of them are really easy to understand, and you can always ask the community if you're in doubt (visit the XDA App Stores forum for your questions about Google Play, as well as experiences and impressions with it).