Recently I was lucky enough to get a helicopter ride for free (something that is not at all common here in Switzerland, maybe in the US it's easier), so here are a few pieces of advice in case you get invited to one (or decide to pay for it).
- helicopters are rather small, so you may not have the leisure of being able to swap lenses. Stick to one type of shot, or make a tradeoff in quality by using a superzoom lens
- ask the pilot what the route will be, so that you know on which side of the aircraft to sit. In general you cannot move around during flight.
- watch where the sun is, so that you can take a picture of the shadow of the helicopter during takeoff
- know the area you will be flying above. If you know the route in advance, use Google Earth to do a "practice flight" so that you can recognize the locations when you fly over them.
That's it, I hope you'll find some of this interesting.
For the record, it was an absolute blast. It's like flying in a soap bubble!