As everyone said above, never let your guard down. There is 2 types of instructing in multi. High alert and very high alert. I've had great students start to spin us on the power on stalls, students try to feather the wrong engine, feather the prop on the ground, you name it.
Just be alert at all times. Especially for power on stalls, accelerated stalls, and engine failures at low altitude. It also depends on the trainer, because ones like the aztec are one of the most forgiving aircraft with a slow spin entry, which is easy to detect.
Be extra alert on the new PTS for accelerated stalls. I haven't had anything bad happen yet, but this maneuver is probably my worst fear. Be absolutely sure the ball is centered as said before.