keep your elbows or forearms on the table balance the pinky of the hand you are painting with onto the clients hand , this is called balance point positioning it will stop you from being shaky and help you to be more precise in your painting ,
apply your first layer very thin , this will guide where your second (slightly thicker ) coat will sit.
Buy some nail fresh and a small detail paint brush , use that to swipe in and neaten up the smile line .
stay calm .