The Seneca II POH recommends three twists of nose up trim on final, to help in the flare. Also some schools bung 50l of water in the baggage compartment if you're flying around 2 up. When you chop the power in the flare, the nose drops like a rock, so haul back (hard, its heavy) on the control column, and do not let it forward. I almost crashed once in Sedona doing this, let the nose drop and we started bucking around like mad. They say that on the third bounce the under carriage normally collapses, so I count myself lucky
Nice aircaft to fly, Seneca I is a bit of a dog, the II is great though (not flown any of the others). SE ceiling of ~13000, climbes fine two up on one engine, on both it is a beauty. If you have never done a power on stall in one, my advice would be to slow down before applying full power. Otherwise you'll become Chuck Yeager with your nose pointing about 50° up. Its ok, just you loose the horizon. If flying a turbocharged one (the II), be careful not to overboost the engines (ie. don't firewall the throttles). I open it up to 25" on the brakes, then release the brakes and increase MP to 39" on the roll. You may find one turbo kicks in before the other and you *may* get some yaw at the initial roll. No biggie though.
Have fun!
EA