Mostly you just have to be good at knowing how to partition calculations in your head, which is mostly practice. You don't for instance go through the long procedure for multiplication for something like 1008x1009, you break as 1000+8*1000+9 and it becomes 1000²+ 8x1000+9*1000+8*9 or 1,017,072, which is a hell of lot faster usually, even then punching it into a calculator especially if it's not switched on in front of you. These aren't really 'tricks', math is basically nothing but tricks, and much of physics is learning them and getting practiced at dragging them out and adapting them.