First apply ink to your image and ensure its on a stable surface. You need to use a very fresh ink pad so the ink stays wet a while.
Starting just off your image (left or right depending on which hand is your preference - I'm right handed so work right to left) in one smooth movement roll your brayer over the stamp while the ink is still very wet. This should give you a perfect image of your stamp on your brayer.
Again, in one full and smooth movement, roll the brayer with the stamped image in one direction (doesn't matter which) onto your cardstock. What I would say is that it's a bit tricky to get it where you want it, so always start with your "mirror" image first and add the normal one after. It's quite tricky on a one layer card - you may need to "trim" to fit the space you wanted (here I used a full sheet of A4 folded in half and cut it to size after - quite a bit of wastage so perhaps a better technique on a layer you can cut out (or perhaps someone else knows a trick I'm missing for getting the brayer lined up where you want it!)
Now add your "normal" image where ever you want it - as the ink transferred from the brayer will be lighter, its best to take off the excess ink from your stamp before stamping it out - I forgot here so you can see my normal image is much stronger than the mirror.
Decorate, add your sentiment - et voila - mirror image - in the words of the meercat "simples".
I expect to see lots of mirror images from the LIMettes now!