Tactics
Initial setup
Flag Positioning
There are about 5 main ways to position your flag on the board:
In a corner surrounded by 2 bombs. Surrounding the flag with bombs means your opponent will have to get a Minor safely deep into your territory to win the game this way. A corner flag only uses two bombs and leaves four to position elsewhere in your ranks. These two reasons make this the obvious place to put your flag.
On the back row surrounded by 3 bombs. Using up an extra bomb will give you the freedom to place your flag anywhere on the back row, making it harder to guess where it is placed but still requiring a Minor deep in your territory to have it captured.
In the middle protected by 4 bombs. This gives an even greater freedom of placement but sacrifices most of your bombs, places your flag closer to your front lines, creates a larger area for you to defend and effectively divides your defenses in two by allowing only a one space gap for pieces to move through..
Anywhere in the ranks, Unprotected. Without the protection of bombs you have total freedom to place the flag anywhere on the board . It also makes your flag much harder for your opponent to identify by looking for a group of pieces that never move.
Unexpected places. This one is in the front row, but is still protected by bombs. Most opponents will not spot the lack of movement from theses pieces and guess where the flag is placed. In fact my brother once accused me of cheating by moving my flag because I had moved every piece in the back rows of my lines. He couldn't work out where to attack.
Bomb Positioning
Places where people don't expect bombs to be positioned. Apart from making it difficult to take your flag, I think the real role of bombs is to deter your opponent from doing random attacks into your lines with high value pieces. To maximize this deterrent, I suggest placing bombs in an almost totally random way, making it hard to guess when not to attack. Behind the lakes is a very random place to put a bomb and so is in the back row, especially when your opponent has identified your flag already.
Flag decoys. An arrangement like this can cause your opponent to pointlessly expend effort attacking in a corner only to find he loses Miner for no gain. There is an added psychological warfare benefit if you act out the part that you are about to lose the game when he goes to take one of the bombs. You opponent will usually get quite distracted that you are messing with them.
You can also create a flag decoy effect by simply not moving the three corner pieces through out the game. You might want to position lower ranking pieces here as higher ranking pieces are often needed during play.
Spy Bluffing
The easiest way to winning the game is to have the highest ranked pieces on board by eliminating the enemies. An aggressive opponent might attack with his Field Marshal. Even if they don't attack with it, at some point in the game, the Field Marshal is revealed. Your goal should be to eliminate this piece with your Spy. My first move after the Field Marsh is discovered is with a piece I will call the decoy Spy. I use this piece to aggressively chase the Field Marshal away or sometimes into the mistake of moving next to the real Spy. If you play against the same opponent regularly, and use this ruse often, you can sometimes move the real Spy and they will believe it is a decoy and ignore it or try to move in to attack it, to their demise.
Obsolete Tactics
Because of the advent of the screen, a small range of deception tactics relating to the laying out of the board are no longer of value. Most people design their setup by initially placing the flag down first, then surrounding it with bombs and so on. When this is done in plain view of your opponent, it can gave them the idea of where to look for your flag. You can use this knowledge by setting up a decoy flag first and placing your real flag later. This tactic has two advantages, they spend a lot of their time concentrating on one area of your board sometimes ignoring your attacks on them because they think a quick kill is on the cards and second they are prepared to make larger sacrifices of pieces to get to the dummy flag area than if they were just probing your lines and this can be costly when the realize they don't know where the flag really is located.