Congrats flexy!
Now, advice... hmmm...
Definitely take sick bags, but if you want to stop them being sick, either give them control or make them close their eyes, and open all the vents. If you give them a sick bag it WILL be used!!
Make sure they arent flying on instruments in the first few lessons. Cover them up if you need to.
Say as little as necessary.
As has been said, make sure they dont have their feet on the brakes.
Probably the best advice, leave any anger or depression on the ground, and enjoy the flight!!!
Congrats again!