This is one of those silly little problems that doesn't really cause harm but is exceptionally embarassing - did the left for right trick several times learning to drive but kept it together on the test. Coaching youth baseball is also fun - number of times I have pointed authoritively out and said something like "Out in Left Field" only to get a voice saying "Coach...that's Right Field!"
Aerodynamisist - I find that it works better having just one side posted, I can work out the other much more quickly. Having two post-its just adds to confusion - if I think "Left" and look and see "L" then fine - but if I think "Right" and see "L" then I need more time to work it out in my head.
Good way is to get one of those blue plasters that they put on staff in supermarkets, restaurants etc. Put one on my left hand and now I have "Left" and "Not Left". Alternatively - write on my hand or use my watch so I have "Watch" and "Not Watch". I know these seem pretty purile but they work for me.