To get the best value from your half hour is to buy another half hour and make it a whole hours flight. In my experience, half an hour is not enough to get a real good go at flying a helicopter.
I would not worry too much about the throttle at this stage - your confusion basically boils down to different techniques required for different types. Let us know what you are going to be flying and then the advice here will be a little less confusing.
Food for thought:
Before starting my IR, I asked the instructor if there was any reading I should be doing to prepare. He answered by telling me to throw any books I have into the back of the cupboard and chill out. They would teach me all I needed to know.
If I was you, take the advice given here, but walk into the briefing with an open mind - you will get more from listening to your instructor on the day than you will trying to remember what you have read here. No critisim on ppruners, but I've had plenty of overly keen students who wouldn't listen because they thought they knew it all.