Although commonly known as the Union Jack it should really be called the Union Flag, unless it's on a boat. Which I suspect you aren't.
The right way up:
Give the Union Flag a quick glance and it might look symmetrical, but it's not. To support Team GB in style you should have your flag the right way up. If you look closely you'll see some of the diagonal white lines are wider than others. One of the thinner lines should be on the bottom left hand corner (the side your flag pole would be).
So now your know so go forth and wave your Union flags with pride