How to prevent broken bolts?(long thread)

[Bxsvx]

Hello everyone. I am trying to learn certain techniques when fixing automobiles. I have had problems trying to remove old bolts. I know that the two metals, the bolt itself and the other part that fastens to the bolt become one. This happens after aging and corrosion(also other reasons but I forgot). I have read and heard to put lubricants like wd-40, liquid wrench, etc. But when I spray these lubricants, which is usually right away(not a week in advance, and also dont have the time), I feel that it is not penetrating towards the threads, it just coats the head of the bolt. I have on many occasions, have had problems with bolts snapping. Once I overtighted it and it snapped(my mistake). I also snapped a bolt on a ground bolt on the frame of a 92 legend(removing). But most of the time its when removing that it snaps. I have also thought of driving the car towards its normal operating temperature, so everything can be warm and be more easily removed. But then scientfically the bonds in the material expand as due anything else in nature, so wouldnt the thread be different when removed? Wouldn't it shrink back when reinstalling the bolt? Sorry to make this thread long, but I'm so curious, and I also want to take care of my baby's valve cover seals and other seals. Thanks everyone, I hope this thread helps more automotive enthusiasts like myself