The most useful psychological technique I've found is Internal family systems (IFS). If you do it with a therapist, it can be very powerful, and mind bending, like a psychedelic trip. The way it helps productivity is when I can't motivate myself to do various tasks I use IFS to explore what's going on in my brain that fuels that procrastination.
It takes me to memories and dusty corners of my brain that I rarely visit that form the foundations of my identity. The only bad part about it is one really needs a therapist to guide oneself when one goes deep and visits what IFS calls "exiles".