Has to be a laptop? Aight.
Rules of thumb:
Do not buy one that's advertised as thin. Gaming hardware creates a lot of heat, that heat needs airspace and fans to dissipate.
Regardless of the laptop, buy a cooling pad with it, and a carry case that can cart around the cooling pad with the laptop. Your hardware might just last awhile longer that way.
Don't buy a major PC assembler brand. Dell, HP, Toshiba, Sony, et cetera... they're all being outclassed nowadays by regular old hardware manufacturers. Asus, MSI, Acer, et cetera.
Aside from that, what the other people said, mostly.