There are a few things you should do when preparing to ship your boat.
General shipping tips
Provide the correct dimensions
Manually measure the overall length, height and beam. Any boat over 8’6″ wide, will require an oversized load permit to be legally shipped. A boat over 12' wide will require an oversized escort.
Secure all loose gear below and above cabin. Close and secure any hatches, windows, doors, etc. Tape anything closed from the outside. Secure all anchors, life vests, etc etc inside of the boat.
Drain fuel and water tanks
It is best to drain to at least 1/4 tank. Remove all drain plugs from the hull. Many carriers will require that you fully drain the tank before transport.
Disconnect batteries, and make sure all of the cables are in a secure location.
Pick the proper loading location
Pick a loading spot that has a 14′ clearance.