Well, there aren't too many teas I'd let sit for 5-6 minutes, so that's the first place I'd look.
And I pour straight boiling water on very few teas, although that gets into the "personal taste" arena quickly. I use thermometers, timers, and weigh tea and water down to grams and cc's when I'm feeling fussy.
The rest is just trial & error. And good fun.