Avinash is always good for marketing analytics advice, so no surprise he has some gems for picking success KPIs.
To correctly identify the impact of your campaign, pick the business outcome you want as the Success KPI and not one of the many driver metrics.
Driver metrics are easy to game. Ad clicks vs. site sessions. Conversion rate vs. revenue. Social followers vs. actual customers.
Measure what you actually want to happen. Not what you think might in some way be correlated with what you want to happen. (Yeah, sometimes it can get fuzzy, just do your best.)
You cannot move an unmovable metric.
For your own sake, pick something you can actually impact and influence. I don’t think Toyota’s marketing department is going to move the needle on their reliability reputation at this point. Don’t be Sisyphus.
Ideally you settle on something that moves the business forward if you succeed, but also allows you that room to succeed.
And while you’re at it, pick one for brand efforts and one for performance efforts.