While creating a Power Pivot based report i.e. Pivot table or Pivot chart, using Month slicer is a very common requirement. There are number of blogs that shows how to sort the Month in natural order in Pivot table, you can also found some workarounds to sort Month in natural order for slicer also. One such tip is explained well in MSDN blog here.
But with Excel 2013, there is not need to have such workaround.
Assuming that you have Date table with following columns
Year => 2010, 2011, 2012.......
Month Name => Jan, Feb March.....
MonthOfYear => 1, 2, 3..... 12
Now select the column Month Name, under sort and filter section of Home tab.
Now click on "Sort by Column.."
In this select the Column to be sorted and sorted by. Here, sort column is MonthName and By column is MonthOfYear. Click Ok.
Now you can add the Slicer of Month Name and it will sorted by natural order instead on alphabet.
Using this functionality,any column can be sorted by any other column within the table.