for the original pattern, if you start with the lowest rectangle (with an L shaped shaded region) and count up to the third rectangle... that rectangle does not have the same shading as choice B (in B, this is the middle rectangle and thus the reason it's wrong).
as far as the second pattern... i was never very good at these. i would spend a few seconds folding it in my head and rotating it and if i couldn't find the answer quickly then i would guess and move on.