What are some ways other than in-person tests that webmasters can do to try to increase user conversion and participation?
A/B tests and multivariate tests allow comparing the implemented content/design with an alternative. A script will randomly show the user either the original content/design or one of the alternatives. A back-end web software will allow the webmaster to compare how effective is each version by relating the presented content/design with accomplished goals.
After a while (from a few hours to a few weeks) the webmaster can decide ending the test and adopting the best alternative, and if he/she wants start other tests.
A free and popular online software is Google Optimize.
I have read many good things about Popup Domination 3 (a brand new version).
This is not an affiliate link and I have no vested interest in the product. I have just purchased it and it is dead simple to implement.
You can time when during your pages' presentation to show a popup asking for contact info from your visitor. Having a static sign-up form on your page is nice, but the author's claim a much higher rate of participation with the popup technique.
I feel, personally, that popups are annoying, but depending on your audience they might work much better.