Make sure you have a PFD onboard, and since you are a little nervous about the water, wear it. Take binoculars if you have them. Take a water bottle or Camelbak along, and a snack. Wear sunscreen and bugspray (or at least take the latter in case you need it). Don't try to do too much your first time out because you will likely be sore afterwards.
I always used an old pair of bike or weight lifting gloves as I found that I got rubbed places on the inside of my thumbs after paddling for awhile.
Other than that, it's really quite easy and fun and not hard to pick up at all, on flat water at least. Just go with an open mind and enjoy!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow