I haven't actually read GTD probably because I have always been very pleased with my productivity output and I always get things done. Though, I plan to read that book around 10 months from now where my calendar eases a bit.
I keep things simple and identify which is
important vs urgent. The link is a post I wrote a while back about working on urgent matters first. In an excerpt:
When people are faced with tons of workload, confused, they usually asked themselves what they need to do first; most people struggle to identify and act on what is urgent rather than what is important.
I have read and attended ton loads of time management trainings and while they are good, I'd rather keep my philosophies simple: urgent vs important. Life is too complicated already. This works for me and see if it works for you also.