There are three places it would be nice to have plaid match, but unless you alter the pattern or are very lucky you’ll probably only manage two out of three.
The 3 areas are: Horizontally across the two front panels. That is to say, if you follow a line of plaid across the body from left to right it should match.
2: Vertically across the front overlap. Such that the pattern where the fronts overlap and fasten is the same width as any of the vertical sections on either side.
3: The shoulder seams. Good luck on that one! 🙂
To get the horizontal match right make sure both fronts and the back are cut such that the bottom and the side notches are positioned on the plaid so that they all match.
For the centre to match (matching type 2) you need to make sure the center fronts are on the same position on the plaid vertically. From memory the centre front is marked with a notch. If not you can find it by overlapping your traced pattern pieces as if they were buttoned up.
Hope that helps.
Oh and I always have a glass of red wine on hand for tricky pattern matching. Works for me. 🙂