There are a few ways to scale and optimise earnings, lets go over 2 things you can implement quickly:
1. Expand into Countries outside the USA
Lets say you're doing a diet product promoting it in the USA, that product earns you 100% ROI. That means you spend $100 to earn $200 revenue, thats $100 profit.
(In Pay Per Click marketing, such ROI is quite typical. You will find some elite PPC marketers able to spend $500 to earn $2500.)
The simplest way to scale, would be to create a SEPARATE campaign and target another country, say the UK.
Do not mix up the campaigns demographics up. I never do it that way, and I doubt the elite PPC players do it too.
So, UK has one campaign, USA has its own campaign.
In this way, you will be able to see which country is giving you the clicks and it will be alot easier to optimise the campaigns by cutting out keywords that do not convert.
…which brings us to optimsation using conversion tracking…
2. Conversion Tracking
The way to cut out keywords that do not convert is to have tracking in place. Otherwise…there's just no way to spend $500 to earn $2500 if this is not placed.
If you're using Adwords, good news is, Adwords comes with a conversion tracking pixel. Just paste that on the thank you page and once a sale occurs, the keyword that lead to the click, which lead to the sale, will display "1" under the conversion Tab. After a few days, simply pause all keywords that do not have any conversions. Quickest and Simplest way to optimise.
To Your Success!