The customers you have now are giving money to someone else for something else.
There is something your customers aren't buying from you.
What they buy would make sense for them to have because it makes the experience of what you sold to them even better.
Even if you don't make or own something that your customer is buying, this is something you could make money from.
^^ this is a paraphrased wisdom from Dan Kennedy
When you look at real-world examples, you can see that toysrus “a toy store” carries kids diapers and mom's breast pumps. Why? Their customers are parents…
Although they come there with their kids – they could buy other things that they would need. Thus it makes sense for toysrus to sell.
A couple of years back, I noticed Tom And Stefanie – a kids clothing store carrying kitchen utensils.
Although from the outside it doesn't make sense for a clothing store to carry kitchen utensils, Think from the angle that it's mostly moms who go to buy clothes for their kids.
This is called cross promoting or cross-selling. A different version from up selling.
When it comes to online business, think about your audience what they are buying outside of your arena?
What software do they buy, what subscriptions do they get, what other product would add value to what you are selling your customer?
You could then do one of the following two things:
-> Become an affiliate of that product/software and promote to your peeps
-> Negotiate on a mutual partnership – where you agree to promote their product/service to your audience and they agree to promote your product/service to their audience.
This can instantly boost your revenue without spending loads of time and money.
If it's highly lucrative then you could consider to make your own version of the same product and add it to your product line.