Collect contact information from potential users (e.g. email or phone number). Get them to subscribe to your newsletter to keep them up to date with the progress and launch of your product.

Formspree is a nice tool you can use.

Google Analytics and Hotjar.

Track the number of visitors on the landing page and determine your conversion rate. Analyse click-maps and user recordings.

Share your product's landing page on Facebook, post in relevant groups, Reddit or other relevant social sites (optionally you can even use ads to bring google search traffic).

E.g. screenshots of your posts and their permalinks.

Include a brief comparison of each lead channel, highlighting the one that worked best.