Keep off the beer, take a bottle of cheap lemonade, a couple of sips, not a gob full, before you leave port.
A good nights sleep, a couple of rounds of toast, a big breaky is only for those that have experienced small boat sea fishing.
After breakfast, A visit to the netty, wether you feel like it or not, is a must.
As has already been said, warm dry clothing, you can always take off as you don't want to get over warm, but on a good day it can get very wet and cold out there.
Preparation & preparation is a must, get to know where every thing is in your tackle box, you don't want to be bending over with your head below the gunnel's messing around looking for bits n bobs, as this will bring on sea sickness, for the less experienced boat angler.
If your not catching, don't get down hearted, look around you, see how others are catching, adapt, they will come on for you.
Remember common sense rules, do what the skipper tells you, even at the time it doesn't sound sensible. Your out for a great days fishing, enjoy and think positive that your going to catch that fish of a lifetime, well until the next trip.
Have a great trip, I'm looking forward to reading your first sea fishing, from a boat, report.