Make sure to submit the right .xap file, that will be found:
"My Docoments/Visual Studio 2010/Projects/Your Solution/Your Project/Bin/Reales"
Make sure that the name of your (.xap) file and the name of the application that you entered on the submission form are the same.
Notice that textboxes and text blocks should be visible in both themes of WP, dark and light theme.
by checking the emulator start screen, go to settings tile, then change theme to light and test your application.
Do not use brands, logos or registed trade marks as your icon or as a part of it.
the selected language in the submission form should be the same with the language in the assemply info file.
What if my language is not supported?
If your application language is not supported select "English"
*Please notice that English != English-US || English-UK
*AssemplyInfo.cs can be found in your project folder/properties.
When capturing application screen shots be sure that no debugging numbers appearing on the right up corner of the emulator.
to do so, stop the debugging the application from Visual Studio and run it from the emulator's start screen instead.
Feel free to use Try-Catch blocks in almost everywhere, you don't know what may happens.
and remember: To err is the developer, not to forgive is the user
If you put more than 3 ad controls on the same page.
Your application will fail. so don't.
Good luck with your testing