1. More is more
There is a direct correlation between the number of icons a designer has on the site and total sales. Quality is also very important but the ideal scenario is to have a lot of high quality, unique icons.
2. New Styles
Line and Filled-line icons are very popular right now. Icon design trends can change rapidly (every time Google or Apple changes styles). It is important to keep up with the trends which translate into customer demand.
3. Tell Stories
We have observed that icon sales are trending towards more complex icons that tell stories or depict actions. Whereas "noun" icons used to be popular, "verb" icons (showing actions) seem to be selling more.
4. Distinguish yourself
Icon design seems to be self-influencing in that when a particular style or color scheme becomes popular, everyone copies it . Try branching out into some completely new styles to make your icons stand out. This is risky, of course, so start small and create an SEO set that is completely different to see how it goes.
5. Promote yourself
Incorporate as many channels as possible in promoting your work from Dribbble to Pinterest, FB, Twitter, etc. The more people who know you sell icons, the more customers you will have. It takes a while but building your following up on social media, specifically with potential customers (designers, app developers, etc) will have a positive impact.
6. Do some guest blog posts
If you have an idea for an article for our blog that you think will be interesting to potential customers, write up a summary and email it to firstname.lastname@example.org. This is a great way to get exposure.
7. Post new icon sets regularly
Keeping a good pace at uploading new icon sets will give you more visibility. You can be featured on our frontpage and also on your Iconfinder followers’ front pages.
8. Come up with better tags
The ideal number is between 4 and 7 tags per icon and it can make your icons rank better in the search results. But be careful in not spamming your icons with tags, as that will influence your sales negatively.
9. Focus on sales to Pro users
Creating cohesive sets around themes that will appeal to Pro subscribers. A Pro user is probably looking for icons for a project so theme-focused icons for common types of projects will be appealing to Pro users. They are usually looking for large families of icons of the same style from where they can choose all different icons without worrying about consistency of the final result. Having the same icons in several styles helps too as it also increases the number of icons you have for sale (remember, more is more).
10. Choose appealing colors
Garish, overly contrasting, loud colors can hurt sales. When in doubt, use a color combination chart such as Google’s Material Design color chart or any of the tools listed on http://www.creativebloq.com/colour/tools-colour-schemes-12121430
11. Listen to your users
Keep an eye on the comment section under your icon sets. It is not uncommon for users to ask for some additions to the already existing icon sets. Since this is direct feedback from the users, this is one of the best insights you can get on what might be missing. Offering a consistent icon set with a complete set of icons that users need will distinguish you from the rest of the icon sets in that category. Also, your customers can contact you for specific projects they need your design skills for. It is a good source of opportunities, so keep your ears open.
12. Consistency across style and theme
Have many icon sets or larger icon sets consistent in style and themes. Having a broad offer of icons that are consistent between each other is a great thing. This way, even the pickiest users will be able to find a group of icons that they can use on the same website without worrying about them not matching.
13. Do variations
Have the same icon sets in many different styles. This has to do with the #1 above. Having a variation of the same icon in several style also increases the total number of icons you offer and the chances a user will like any of the different styles you offer.
In case you are experiencing decreasing icon sales, check out this other article for more tips: Decreasing icon sales: What to do?