When submitting your application to the Windows 8 store, you'll have to comply with these certification guidelines:
http://msdn.microsoft.com/en-us/library/windows/apps/hh694083.aspx

Make sure your application passes and specifically watch out for these:

4.1.1 Your app must have a privacy statement if it collects personal information
The privacy policy is super important. Let's say you created a basic application where you input some data and get results from a webservice. Nothing fancy right? Well, you need a privacy policy to indicate what you're going to do with the data the user submits to the webservice. Is it stored? logged? published? etc.

When submitting your app, you can indicate the URL of your privacy policy. It should be somewhere on the web so possible buyers of your app can read it before using the app. This link will be presented in the Windows 8 store with your app.
But you also need to have a privacy policy inside your application, and it should be easy to find for the application testers. My advice is to create a Privacy Policy item in the settings menu (charm bar). That's where the application testers will look first.

**4.5 Your app must protect customers from unintentional large data transfers over metered networks
**Is your app downloading large amounts of data? You're required to show an indication that the user is on a 3G connection (metered network) and that he might be charged for data usage.

You can check the connection type of a user with this line of code:
var networkCostType = NetworkInformation.GetInternetConnectionProfile().GetConnectionCost().NetworkCostType;

6.2 Your app must have a Windows age rating, and you must submit third-party ratings for your app if you have them
If you want to make sure your app passes, choose a high age rating. You might think your app is suitable for 3+, but the app might load content you don't have control over (rss reader, streaming video's). Or submit (personal)data to a webservice.
An age rating of 12+ will do the trick to get your app certified.