I think you need something like this:
declare @table table
(
DateStr varchar(10)
)
insert into @table values('2013-Jan')
insert into @table values('2013-Oct')
insert into @table values('2012-Jan')
insert into @table values('2012-Oct')
insert into @table values('2012-April')
insert into @table values('2013-April')
select * from @table
order by CONVERT(date, DateStr+'-01') DESC