Requested WoW macro

I play a shadow priest, and can’t seem to get my dps up to save my life. I’ve played with different spell rotations, and while they seem to get better, nothing hits the mark. I would like something that will automatically give me the best spell rotation for the highest amount of damage, and possibly to see if there is a way to automatically target the next best enemy under 100% health if my target dies before I cast. Is that possible? The current spells that I use are Mind Spike, Mind Blast, Vampiric Touch, Shadow Word: Pain, Devouring Plague (if I have three shadow orbs), Mind Flay when all else fails or for cooldown, and Shadow Word: Death (if enemy target is under 20% health)