No need to fully warm up the car before moving. In summers, may be wait 20-30 sec, and in winters like 40 sec to 1 min and then slowly move. Make sure not to rev up aggressively when moving from acold start. Keep the RPM under 2000 until the blue light is off.
At signals there is no harm in staying in D but i always shift to N so that my foot is free. In D, the power is going to the torque converter and cuts off in N. There is no harm in staying in D while waiting but what's the need? Shift to N, apply hand brake and khud b relax karo or gari ko b honay dain.
If signal is long i shut down the car while staying in N and applh hand brake. Better to to do it in P but then the car unlocks which I dont lile while waiting at a signal especially at night.
Lastly, when parking always apply hand brake first with N gear and then shift to P and shut off so that the locking pin doesn't bear the veh load when it is standing at a slope.