Different aircraft have different requirements (electrically speaking) to get the most accurate reading on the standby compass, so there is no hard and fast rule about that.
Regarding switching pitot heaters on, remember that venturi effect will provide cooling. It costs nothing to switch it on (unless you're stationary on the ground for hours while the stude goes through the run-up checks), and will cost lots if it gets iced up in the air. Besides, it's a good habit to get into.
Finally, on the use of the transponder, if you turn it on, for heavens' sake make sure you're squawking Mode C. Nothing gets the heart rate up if you're trogging along at altitude and you get the "Traffic - Traffic" callout and no Mode C info to tell you where to look. I have known instructors who tell studes to sqawk only Mode A on the grounds that they can't get done for straying into controlled airspace. And yet they call themselves professionals!
