Quick way to factor difference of two squares

Good Evening,

I am working on factoring the difference of two squares example: 12b^2-300 and understand that the 12 breaks up into (3b ) (4b ) or which ever numbers it breaks into but I am spending so much time figuring out which numbers go in the parenthesis to make the equation fit back to the original. Does anyone know a quick and easy trick to find the factors that will go back to the original equation?

Thanks in advance.

12b^2-300

Factor out 12:
12(b^2-25)

Factor the difference-of-two-squares:
12(b+5)(b-5)

That comes with practice. You may use the process stated above.