What is the fastest way to increase online sales?

Sell again to people who have already bought. It is faster than any acquisition channel because the expensive step — earning trust — is already paid for.

The reasoning

Concretely: work out the median gap between first and second order, and reach those customers slightly before it. Most stores have this data and spend the budget on strangers anyway.

What most people get wrong

Traffic is the expensive problem and conversion is the cheap one. Doubling a 1% conversion rate is usually easier than doubling visitors, and costs nothing per month.

Retention beats acquisition on every measure, and almost every store spends the other way round.

The slowest part of most mobile stores is images nobody resized. It is the most common performance problem and the easiest to fix.

How an app changes it

Push notifications are the one growth channel you do not rent. Every other route to a customer is paid for again each time.