edit: note, question 288805 is similar, however, I specifically am asking how does MSTest choose the default test order. Please
The MSDN says ;-)
How to: Create an Ordered Test
http://msdn.microsoft.com/en-us/library/ms182631.aspx
MSTest.exe command-line options
http://msdn.microsoft.com/en-us/library/ms182489(v=vs.120).aspx