Performance Rules of Thumb
The 3:1 LTV to CAC Ratio
You should aim to make at least 3x the profit off a customer compared to what you spent to acquire them. Below 1:1, you are bleeding cash.
The 2% E-com Benchmark
The global average conversion rate for a standard e-commerce store is roughly 2%. If you are converting below 1%, focus on CRO before increasing ad spend.
The A/B Test Law
Never stop an A/B test before reaching at least 95% statistical significance, regardless of how "obvious" the early results might look.