LOL    ;D

           I don't know any tricks to getting the paint on right without a steady hand .

                   You can mask it  .   Might take a little bit but re-positioning tape is easier than continuously cleaning up over-paint  .    

                     --  You can use a second , moist brush or the tip of a paper towel  to clean up mistakes as you go if you don't mask -- 

             Try resting your brush hand different ways  , like on your other hand or wrist , a book etc  till you find a style that gives you the most control .

                          I can't believe that I know a guy that's gonna have work in the Smithsonian !

                                        Crazy   ;D