Tornado Stance is fairly useless altogether in combat. It can be mixed with Lightning Stance for stunning a mass group of enemies at once, but this also drains your health very fast. Although outside of combat its handy for getting around the map quickly.
Lightning Stance is best used with Siphon stance, however this will make you greatly vulnerable.
Siphon Stance is best used with Turtle stance as it really gives you the power to tank massive damage quite easily. If you are nearly out of mana with a large group of enemies coming your way it's best to deactivate Siphon right away since it costs less mana then Turtle, and when Turtle turns off you have a change to take massive damage as your defenses are greatly lowered.
Turtle Stance is useful on its own, but its even more useful tanking a lot of damage with the help of Siphon stance as stated above. It's best used when moving in the direction that the enemies are coming from. This way they will be coming towards you, making up for your lack of speed, and will refresh your mana quickly as you charge on through the massive wave.
Battle Leap is good for crossing wide gaps or going up big ledges in one move. But be careful that there isn't anything in your path. One object out of place could send you sailing to your death.
Battle Pound is best used in very big clumps.