Most important tip? Dunno about _most_ but here's a few to keep in mind...
For Alaska (especially end of August), take layers of clothing. Probably don't need a heavy winter coat, but at least a waterproof layer, some fleece, maybe take long underwear.
Cabins generally only have one outlet, so if you take things that recharge, you might want to bring a small power strip.
Take the stairs - it's generally faster than crowded elevators and you can work off all that food you'll be eating.
Read the ship's newsletter every night before bed so you can plan your following day.
Remember - it's a vacation and should be fun...if there's boring people at dinner or loud people in the hall when you're trying to sleep, ignore them and enjoy life.