Which way does the sign go?

The book I am working with makes a big deal about knowing which way the sign goes in operations of addition and subtraction.

I would say just try to work it out logically in your mind

3+4 = 7
3 + -4 = -1

This can get confusing when you subtract a negative number
3 - -4 = 7

This is probably one case where memorization works since it is hard to intuitively see that subtracting a negative number is the same as adding it. So just remember that when you subtract a negative number to just change the sign to addition.