For me... my results are as good as my plans. I cannot "wing" it, cant flesh it out as I go, no napkin sketches for me.
I design the entire build in sketchup, I design it precisely, I render the dados and the joints. Then when I go into the workshop, I only need to accurately produce what I sketched.
To that end, Ive gotten pretty good at cutting an exact size, a big peice of that might be tools, good measuring devices, and thing like a miter saw, table saw, planer; they allow me to shave wood with no margin of error. so when it comes time to assemble, its like assembling ikea furniture, ever piece just right to fit together.