It's easy to presume that any subject will market. And to an extent that is true – you need to appear at the wide variety of themes. But there is a difference between selling digital products it once and selling something.
Image Source: Google
I'm guessing that you are selling the products that you create on a daily or hourly basis.
You want to do some research to do so.
If you're feeling keen and do not mind you being shown a figure that is really the midpoint of a range of numbers by a computer then the Google Keyword Planner can be.
I used to use it in its previous incarnation (the Keyword Tool) but I find that it only provides a “finger in the air" approximation of the likely volume of searches. And you want to be near the peak of the page to get a portion of the figures.
I prefer to work backward.
The best way to find tips is to learn what people are ready to spend money to obtain the solution and are interested in.
At its heart, the search procedure is that easy.
Utilize the suggestions that appear as you type as a guideline that is great. They are based on real-world hunts and are as close to real time as you are likely to discover.
If a vast majority of these suggestions include the term “free" then it is probably worth noting your chosen marketplace.