I have been selling WordPress plugins for 3 years and currently own and operate a small WordPress plugin marketplace.

Hands down the best way to reach new customers is via a free version of WordPress.org. That said you do need to be careful not to give too much away for free. If you need some specific advice on that let me know.

Also it is definitely useful to be a part of a marketplace. Choose wisely! If you need some advice about that let me know as well. :) Setting everything up correctly is essential in maximizing your sales.

Happy selling!