This macro will cast Auto Shot and Steady Shot in alternating order, preventing players from accidentally clipping Auto Shots while attempting to cast Steady Shot. To do this, you must spam this macro, or press it repeatedly and constantly. An easy way to do this is by binding it to the mouse wheel (scroll the mouse wheel in the intended direction after clicking the Bind Key button; a mouse wheel click is treated like a mouse button click, so by scrolling the mouse wheel you can then spam the action in rapid succession). The sequence will reset after obtaining a new target or after two seconds of idle time. It will also cast Kill Command every time it's up, excellent now that it is both off the global cooldown and will not push back Auto Shot.

#showtooltip Steady Shot
/castrandom [target=pettarget,exists] Kill Command
/castsequence reset=2/target !Auto Shot, Steady Shot
/script UIErrorsFrame:Clear();

Previous versions had several UIErrorsFrame commands to hide and clear error messages. However, just having the Clear at the end is sufficient to clear these away, freeing up additional characters for modification/additions.

With Wind Serpent's Lightning Breath:

#showtooltip Steady Shot
/castrandom [target=pettarget,exists] Kill Command
/cast [target=pettarget,exists] Lightning Breath
/castsequence reset=2/target !Auto Shot, Steady Shot
/script UIErrorsFrame:Clear();

The following will autocast your DPS trinkets to maximize your damage output (remeber to change the names and order for your trinkets):

#showtooltip Steady Shot
/castsequence reset=120 Bladefist's Breadth,Ancient Draenei War Talisman
/cast [target=pettarget,nodead,exists] Kill Command
/castsequence reset=2/target !Auto Shot, Steady Shot