Code:
/castsequence reset=target Steady Shot, Steady Shot, Chimera Shot, Steady Shot, Steady Shot, Arcane Shot, Arcane Shot,
This would be a very simple castsequence macro. It will cast all spells in that order as long as you keep smashing the button. The reset=target will cause the macro to reset
whenever you change your target.
Resets can also be triggered by other conditions like entering/leaving combat or after x seconds. You would just need to replace target with combat or a number. And if i recall correctly the usual modifieres ctrl, alt and shift work too.
I didn't include Serpent Sting because I can't remember if it's possible to tell the macro to skip Serpent Sting if the target is already affected by that debuff so it would be a waste of focus.
Hope I could help.