Oh Wow what an idiot, I didn't click on the "Tutorials" button in your FAQ! While reading through the post my brain didn't register as it being "clickable" - I was a bit too tired last night, came back late from my shift
Apologies for making you repeat like that!
I too use the grid method - it enables me to get to the fun part faster
And like you say, it's a huge frustration to realize there was a mistake in proportions or other when you're too deep into the drawing.
I should try turning the drawing upside down by the way! What I usually do to check for proportion missteps is to hold the drawing in front of a mirror. It helps a lot, especially for the face outlines (realizing a cheek is abnormally fatter than the other for ex.)