Using a purpose built laptop desk, usually, will prevent most overheating. They generally don't block the ventilation ports. Setting one on a seat, or on a "throw pillow" (Oh yeah, I liked that one) will cover up or block the airflow needed to keep the CPU and other components at working temperatures.
Most laptops tend to get a little warm to begin with. everything is very close together and there's little room for air movement across the CPU, Mobo and associated components. So, as the energy is consumed by the CPU under load and other parts, they produce heat. Heat for CPU's is not a good thing. We all know this. It's even worse in the smaller, more compact Laptops.
Here's a few things I've always tried to do.
Keep the darn thing out of the sun! I have a regular towel that I place over mine and it's keep it out of direct sunlight.
Don't turn it on until the inside temp. matches outdoor temp. Even in a hot environment, laptops do pretty well.
Take care to blow out dust on a weekely basis. Anything that gets in to clog up the air flow hurts. I had an older Dell Laptop that I used for GPS and I left it pretty much in the truck 24/7. Never had a problem out of it's operation except when I didn't blow it out for almost 3 weeks.
That's about all I did.
