What are good placement strategies for Stratego?
I find that the key to Stratego lies in-


Cover your flag with bombs
Kill all enemy miners.
DO NOT MOVE a new piece when moving an old one will suffice.


Of those, I find that #3 is the most crucial.  Most players have a very hard time attacking pieces about which they have no information;  every time you touch a piece, or even visibly consider moving it, you inform your opponent that that piece is NOT a bomb.