Have stacks guard each other
When you build your pieces into stacks, make sure they are within reach of your other stacks. This way, if your opponent captures one of your stacks, you may be able to recapture it quite easily.
The geometry of the board is laid out so that four stacks can easily guard each other almost anywhere on the playing field. You must place the four stacks such that each stack guards (and is guarded by) two other stacks.
Keep track of reach
As you build up your stacks, your opponent will be doing the same thing. If you have a stack of four, and your opponent only has a stack of three, it means you can reach your opponent without being in danger yourself. However, if it is the other way around, you may not be able to prevent your opponent from attacking you.
Counterattack
If you are attacked from a distance, i.e., with a large stack, your opponent will leave behind a trail of pieces while doing so. If you have a large stack that is near enough, you can counterattack along the same path (but in reverse), capturing many of those pieces that your opponent left behind.
Count how many pieces guard a given space
During the course of the game, it is often the case that both players have stacks within reach of a given space. How do you know which player will ultimately prevail in that space? The trick is to count the total number of pieces from each player that are in reach of that space. The player with more pieces within reach can end up on top.
This means that when you attack a space, make sure you have additional pieces as backup. Otherwise, your victory will be short-lived, as your opponent quickly recaptures the space.
Remember stacks of eight
Since the maximum number of pieces on a stack is eight, it is wise to count pieces very carefully. Even if you have many more pieces within reach of a given space, if your opponent happens to place the eighth piece on top of the stack, you're out of luck.
Also, if you have captured many pieces and want to keep them safe, bringing them together into stacks of eight (with your piece on top, of course) can be a smart move.
First get your own pieces back if you're falling behind
If you have lost many more pieces than you have captured, the first order of business should be to get some of your pieces back. Pick as your target an opponent's stack that has many of your pieces within it, but has not yet reached a height of eight. Start maneuvering your stacks within reach of the target.
With any luck, your opponent will not see your strategy, and you will be able to recapture the target stack. In this way, you may be able to rebalance the numbers and go on the offensive again.
Release an opponent's piece in pursuit of a greater goal
There may be a time when there is desirable goal (say, capturing a tall stack of your opponent's pieces), but your only piece with reach has previously captured opponent's pieces underneath it. In this case, it may be advantageous to release those previously captured pieces while unstacking, if it helps you reach the desired goal.
You must be careful while doing this, however. The pieces you release may, on the very next turn, come from behind and capture you! One way to avoid this fate is if you create an invincible stack of eight while achieving your goal. Another way is to make sure the stack you use to attack with has at least two of your pieces on top, so that when unstacked, the released opponent's pieces will be at least two spaces away from your goal.
Consolidate your pieces
Over time, you will end up with stacks containing both your own and your opponent's pieces. This can make it difficult to organize your defense and offense.
The best way to get one of your pieces out of the middle of a mixed stack is with a two-step turn. On the first step, remove a group of pieces (with your piece on the bottom) from the top of the stack, and move them to an adjacent space. On the second step, return all but your bottom piece back to the original stack they came from. In this way, your piece moves from the middle of your stack (where it does little good) to be out in the open (where you can use it).
Attack from the furthest stack first
If you have several stacks within reach of a target space, it makes sense to attack with the furthest stack first. When you do this, the pieces you unstack on the way will build up the closer stacks that are already there. This way, you are left in a stronger position than you started with.
Retreat first for a stronger attack
If you have many individual (unstacked) pieces near your opponent's pieces, you can stack them up over several turns while retreating, i.e., moving the closest pieces back on top of your next closest pieces. By doing this, you create a safety buffer between you and your opponent, and you also build up your pieces into stacks to be used on later turns.