I usually use 90 percent isopropyl alcohol and a tiny amount of Golden acrylic retarder. I'm told the Tamiya brand thinner already contains retarder, so don't add any more if you use it.
I measure my reducing (thinning) solvent, now mainly so that I have a known starting point, and then add small amounts until I get the consistency I want: the consistency of 2% milk. Take your clean mixing container (a small, smooth-sided plastic or glass container that holds no more than about 2 ounces) and pour a little milk into it. Swirl it around to see how it looks in the container as a reference. Drink or discard the milk (or keep a glass of it handy as a reference until you get the knack.)
I usually spray between 10 and 15 psi, depending on what I'm painting. Fine work at low psi, coverage work closer to 15.
Clean Tamiya paints from the brush with Windex followed by a water rinse immediately after use. Once dried, they can be a puppy mother to remove.