What do you optimize and when in search ads?

This might be the most paranoid question of all times. I usually optimize by ad groups by campaigns and never optimize anything at the campaign level such location whenever I optimize an ad group. I just did the above and noticed campaign performance tanked for a week then spiked up right after. Is there a fool proof layered optimization process that I must follow? Such as you can optimize bids but never optimize audiences at the same time...

Thanks,