The 'simplest' transposition method, even for those who have had some degree of musical theory training, often just uses the method of simple writing the 2 scales down, one above the other.

Little plastic 'slide rule's are commercially cheaply available - you just slide to line up the two relative keys and read off the transposed notes and chords.


BTW, when you are doing musical theory training to pass the exams to demonstrate you can do this, you have to practice doing it a lot to be comfortable with it. You don't NEED to do the exams to benefit from doing the practice btw.... :-)