I know what you mean. I also have problems with shaking hand. I found out, that the best time is at least 2 hours after a meal, and at least one hour after a coffe or a cigarette

, and before I start, I just down at the table where the model is, and do nothing, to relax myself.

Works for me

.
The lines on a air tank and a fuel tank are made the same way. Oh, yeah. And I always make sure, that the lower color is completely dry, and have a tischue soaked in Revell Painta Clean, so if something goes wrong, I immediately sweap a silver color ( in this case ) right off. But NEVER make more than only one single sweap, because one sweap won't destroy the lower base color. If you do this more times, some damage might occure in lower color ( in this case with rims, the orange color ).
Bye.