Beacon should always be on when operating the aircraft.
Strobes on when crossing a runway (and landing light if you think it'll make a difference), off when clear.
Strobes and landing light on when cleared for takeoff (or when announcing takeoff on ctaf). If I'm staying in the circuit, I leave them all on until I've landed and cleared the runway. If I'm leaving the pattern, I generally leave them all on until I've reached my cruising altitude to help with bird and traffic avoidance then kill the landing light at cruise. I wouldn't turn off the landing light until at least 1000-2000 agl because your birdstrikes typically happen down there. When inbound, I get the landing light on the descent check and leave it on until I'm clear of the runway.
A little memory aid that you can use any time you enter the runway for takeoff or exit after landing is "Lights, Camera, Action"
Lights: landing light and strobes
Camera: Transponder to Alt or standby
Action: Mixture, Fuel Pump, doors/windows. All of the last minute things you wait to do until you're holding short and you get your clearance. The "Action" part depends more on the particular airplane you fly but try to find a flow that will help keep you from forgetting anything. For the Action step in Pipers I usually just start at the mixture, move up to the fuel pump, and move out to the windows/doors to make sure they're secure. There's not much that's more distracting than having a window pop open halfway through your takeoff roll.
I only use nav lights when it's getting close to dark or when going IFR.
I put the pitot heat on when there is visible moisture present and temperature is below 40 or 45. And I don't turn it off when I pop out of a cloud and then turn it back on after I pop into another one--if we're going to be in and out of the clouds I just leave it on. My CFI likes to flip it off if we've got a 2 minute period of VMC and turn it back on before we get back into the clouds but I find that to be pretty dumb. It takes the thing at least a minute or so to heat up, sometimes a lot longer when it's really cold out and you've got a lot of wind (and not to mention rain or whatever)!
Oh and please don't be the guy that sits there waiting for takeoff at night for 5 minutes with his strobes on while another airplane is sitting right behind him getting blinded by it. Once the next airplane has stopped and I know they see me I might even turn off the beacon out of courtesy if it's actually the red strobe type instead of the older glow or rotating type.