Pretty sure this is posted somewhere, but some common one's are.
-Pinch your nose and try and breathe through it, in a dream you should be able to.
-Flip light switches, light levels in dreams are reasonably constant, so they shouldn't work.
-Look at a digital clock than look away and back, if the numbers change or are unreadable, it's a dream.
-Jump in the air, if you float around or anything, you get it.
-Try to read small text, then look away, same deal as the clocks.
-Look at your hands, to see if they look wrong, try sticking your fingers through your palms.
-Mirrors may behave odly and you may be able to walk through them in a dream, so try tapping on them.