Reading Watching & Learning - Show Don't Tell
One of the best ways I've found to learn what all the screenwriting manuals and books actually mean by the phrase "show, don't tell" is to read a screenplay and then watch a movie. Or vice versa, just make sure you do both.
A good example of this is the screenplay for "In Bruges" and the movie itself. In particular, the revelation of why Ray and Ken have been sent to Bruges by their nutter boss, Harry.
The dialogue above doesn't make it into the final cut and when reading the script compared to the final movie, you can see why. The flashback revelation without the dialogue is SO much more effective than the above scene would've been.
Show. Don't tell.